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Fishes of the open a n a t u r a l h i s t o r y & illustrated guide

UCP Prelims.indd 1 18/08/09 10:03 AM UCP Prelims.indd 2 18/08/09 10:03 AM Fishes of the open ocean a n a t u r a l h i s t o r y & illustrated guide

J u l i a n P e p p e r e l l illustrated by guy harvey

the university of chicago press chicago and london

UCP Prelims.indd 3 18/08/09 10:03 AM The University of Chicago Press, Chicago 60637 JULIAN PEPPERELL, PhD, is one of Australia’s best-known marine University of New South Wales Press Ltd, Sydney, Australia biologists and a recognized world authority on ( © Text: Julian Pepperell 2010 and ), and sharks. Julian has conducted research on © Illustrations: Guy Harvey 2010 these fishes in partnership with universities and governments All rights reserved. Published 2010 for over thirty years and is an adjunct professor at a number of Printed in China universities. He is a past president of the Australian Society for Fish and recipient of the prestigious Conservation Award from 19 18 17 16 15 14 13 12 11 10 1 2 3 4 5 the International Association. ISBN-13: 978-0-226-65539-0 (cloth) GUY HARVEY is a unique blend of artist, scientist, diver, ISBN-10: 0-226-65539-3 (cloth) angler and conservationist. In 1999 he collaborated with the Oceanographic Center of Nova Southeastern University to create Library of Congress Cataloging-in-Publication Data the Guy Harvey Research Institute, providing scientific information Pepperell, Julian G. for effective conservation and restoration of fish resources and Fishes of the open ocean : a natural history and illustrated guide / . Julian Pepperell ; illustrated by Guy Harvey. p. cm. Includes index. ISBN-13: 978-0-226-65539-0 (cloth : alk. paper) ISBN-10: 0-226-65539-3 (cloth : alk. paper) 1. Pelagic fishes. 2. Deep- fishes. 3. Marine fishes. I. Harvey, Guy, 1955- II. Title. QL620.P46 2010 597.177—dc22 2009032290

∞ The paper used in this publication meets the minimum requirements of the American National Standard for Information Sciences—Permanence of Paper for Printed Library Materials, ANSI Z39.48-1992.

UCP Prelims.indd 4 18/08/09 10:03 AM Ccontents

Part one enVironment, bioloGy anD fisheries 1 1 Why fishes of the open ocean? 3 2 The oceanic web of life 6 3 Form and function 18 4 Interactions with humans 25 Part tWo GuiDe to the fishes 37 5 Billfishes 38 6 69 7 Mackerels 110 8 Jacks/trevallies 122 9 Other pelagic gamefishes 149 10 Sharks and rays 172 11 Other open-ocean fishes 224 Bibliography 260 Index 262 Acknowledgments 266

FOTOO Offical Text.indd 5 14/08/09 8:49 AM FOTOO Offical Text.indd 6 14/08/09 8:49 AM environment,Part one biology and fisheries

fishes of the open ocean 1

FOTOO Offical Text.indd 1 14/08/09 8:49 AM 2 environment, biology and fisheries

FOTOO Offical Text.indd 2 14/08/09 8:50 AM Why fishes of the 1 open ocean?

At last count, scientists had recognized ing includes fish that spend their whole more than 31 000 species of fish in the life cycle in the surface layer, or regularly world, by far the largest order of verte- move into this zone. The second group brate . However, of that number, is fish that spend only a part of their life only relatively few, perhaps several hun- cycle in the open ocean. And those that dred species, might be thought of as fishes temporarily visit the open ocean from of the open ocean. Of course, this leads to other habitats comprise the third group. the question of what exactly is the ‘open His three classifications, in a somewhat ocean’, and secondly, what defines the simplified form, are described below. fishes that swim there. Perhaps surprisingly, the open ocean Permanent residents of the open ocean has no widely accepted formal definition. (‘holoepipelagic’ fishes) In the context of this book, it is defined Fish in this category include , as the surface layer of the sea or ocean, sailfish, tunas, dolphinfish, some flying to a depth of about 200 metres. The term fishes, sauries, some pomfrets, ocean ‘open ocean’ also conjures visions of the sunfishes, the pelagic stingray, predatory wide blue yonder, waters well away from pelagic sharks including the shortfin and land masses. In the context of this book, longfin makos, the blue shark, silky and though, we will include in our definition oceanic whitetip sharks and the surface of the open ocean waters over continen- filter-feeding sharks – the basking and tal shelves, as well as waters around reef whale sharks. drop-offs, islands and atolls. Below the habitat of these true sur- There have been a number of face dwellers live many midwater (mes- attempts to categorize marine fishes by opelagic) fishes, some of which make habitat, all of which suffer from the same nightly excursions to surface waters and The outer edge of problem of fluid boundaries. Having said are therefore also included here. Many the Great Barrier that, one system of classifying pelagic species in this category were hardly Reef, Australia. marine fishes, proposed by Russian ich- known at all before the advent of sur- Reef drop-offs thyologist Nikolai Parin, has consider- face longlining – setting lines with hun- such as this are able influence on the fishes selected for dreds or thousands of hooks suspended prime habitat for this book. Following Parin, I’ve grouped by buoys. This gear, set around the many open-ocean fishes into three categories according clock, not only catches the main tar- species of fish. to the proportion of their lives spent in get species (tuna, , sharks) but Julian Pepperell this open-ocean zone. This first group- also an assortment of these midwater

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FOTOO Offical Text.indd 3 14/08/09 8:50 AM fishes. These include , oar- Dwellers of the open ocean for only part of Floating logs and fishes, opahs, the louvar, and some of their life cycles (‘meroepipelagic’ fishes) debris provide the snake mackerels (family Gempylidae) important Fishes in this category might spend only such as the oilfish, escolar and the snake habitat for their adult lives in this zone, or at least mackerel itself. both permanent part of their adult lives. Examples would Other types of fishes in this category and temporary include Atlantic and chinook salmon, strongly associate with surface materials, residents of the which enter the surface layer of the such as drifting weed, debris, logs or even open ocean. open ocean only as early adults, having drifting invertebrates such as jellyfish. Julian Pepperell migrated from fresh water. They feed and Examples include the tripletail, pelagic mature in the for a number leatherjackets and oceanic puffers. And of years before returning to freshwater finally, the pilotfish, a small member of rivers to . Other species in this cat- the jack family, spends its life swimming egory included here are the whale shark, in close proximity to large pelagic fishes, which is mostly oceanic but gives birth especially oceanic whitetip, blue and in shallow waters, and some flying fishes, whale sharks. The remoras have adopted which must attach eggs to floating algae a similar habit, but, rather than swim such as kelp. Another group of fishes in near large hosts, they attach themselves this category spend only their juvenile by means of highly modified dorsal fins phase in the surface layer. A good exam- and are therefore passively transported ple is the bluebottle fish, which spends with their hosts to cover the same geo- its juvenile life in close association with graphic ranges. the floating colonial siphonophore, the bluebottle or Portuguese man-of-war, but when mature, takes up a benthic (bot- tom) existence. Two other major groups

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FOTOO Offical Text.indd 4 14/08/09 8:50 AM included here are some members of the spread, either occurring on both sides of jack family, Carangidae, and several of ocean basins, or at least around offshore the Spanish mackerels (Scomberomorus islands. Fishes in this category include the spp.). Many jacks are found as juveniles bluefi sh, bonefi sh, tarpon and roosterfi sh, around fl oating objects or buoys, while a number of carangids (permit, queenfi sh, the juveniles of some, such as the golden and some jacks/trevallies), most of the trevally, mimic the pilotfi sh in looks Spanish mackerels and several sharks and and behavior, and in so doing, probably rays (bull shark, and spotted obtain similar protection and dispersal eagle ray). by swimming with their larger, highly While relatively few fi sh species have mobile hosts. adapted to life in the open ocean, those that have tend to be very successful. Many occasional visitors to the open ocean of the species included in this book have (‘xenoepipelagic’ fishes) fully global distributions, occurring in all These are either coastal pelagic fi shes three major as well as the Mediter- which move offshore from time to time, ranean Sea. The fi shes of the open ocean or coastal species that associate with depicted and described in these pages fl oating mats of weed or debris and drift include the largest fi shes on the planet – into the open ocean as a result. Fishes in the whale shark, the basking shark and this category included here are some of the manta ray. They also include the larg- the leatherjackets, chubs and some jacks, est bony fi shes in the world – the oceanic including, for example, the amberjack. sunfi sh, the blue marlin, the Finally, also in this category are some and the Atlantic bluefi n tuna. Some spe- species of fi sh which are normally coastal cies, such as the streamlined wahoo and but which move offshore to take advan- the sailfi sh, swim faster than any others, tage of upwellings of nutrients or plank- while several of the billfi shes and tunas tonic blooms, such as various herring and and sharks make regular transoceanic, sardine species. or even interoceanic journeys. Some of While these categories have helped these fi shes, such as the skipjack tuna, are guide the entries in this book, there among the most prolifi c fi sh species on remain some exceptions and outliers. A earth, supporting huge commercial fi sh- number of commercially or recreation- eries that supply millions of people with ally important species are largely coastal affordable protein. The fi shes of the open in their habitat preferences but may be ocean are remarkable in many ways and encountered at the edge of the open-ocean it behoves us, as stewards of our marine habitat and are therefore included. In resources, to manage and conserve them these cases, a general criterion for inclu- sustainably for the benefi t and wonder- sion is that the species should be wide- ment of all who will follow.

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FOTOO Offical Text.indd 5 14/08/09 8:50 AM The oceanic 2 web of life

There is an apocryphal story of an angler and animals within a vast, but relatively fishing one pleasant morning with high closed ecosystem. Here, we will explore hopes of a great day’s fishing. He hooks the food web of the focus of this book – the first small baitfish of the day, but the food web of the upper layers of the as he’s winding it in, a bonito takes it. open ocean. As the excited angler attempts to land the unexpected bonus, a big yellowtail Ecosystems of pelagic fishes promptly grabs the bonito. The sudden Pelagic fishes live in a somewhat unusual screaming of the little bait reel loudens environment, often far from land, with even more when a large little if any physical structure available. engulfs the yellowtail in one swoop and This habitat has been likened to a marine heads for the horizon. The ensuing fight desert, since the availability of food is is long and hard, and then, just when the often very patchy, dependent on transport tuna is nearly within range of the gaff, a of nutrients from the land or in upwell- huge blue marlin appears from nowhere, ings from the abyssal depths. Some areas swallows the tuna and so the fight is on may be rich in nutrients, and therefore again. With incredible skill, and by this are hotspots for marine life, while oth- time, well out to sea, the angler finally ers may not contain much life at all. This has the catch of a lifetime alongside the world in which open-ocean fishes live is boat when suddenly … the little baitfish a complex self-contained ecosystem that spits out the hook! Now, even if you maintains a rich and diverse fauna and don’t believe this fish tale, it does illus- flora on a vast . This environment trate the simple concept of a linear food extends from the ocean’s surface to per- chain quite nicely. Old textbooks on biol- haps 200 metres below – in reality a mere ogy often referred to these as food chains, film on top of the world’s great oceans. in which each link connected different But this thin and delicate layer contains organisms in a direct line. But in reality, the stuff of life – sunlight, oxygen and the way that organisms rely on each other warmth. for food is far more complex. Hence the The building blocks of all oceanic term ‘food web’ was coined, quite aptly food webs are the phytoplankton – tiny relaying the idea of an intricate inter- single- or multi-celled floating plants dependence of a whole suite of plants which manufacture sugars by photosyn-

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FOTOO Offical Text.indd 6 14/08/09 8:50 AM Top Tiny phytoplankton and zooplankton are key building blocks in the oceanic food web. seapics.com/ iq3-d/Peter Parks

Middle A feeding frenzy of small tunas sends signals to other predators such as sharks, dolphins and seabirds. Julian Pepperell

Bottom A searching gannet hunts for surface-feeding tuna. Julian Pepperell

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FOTOO Offical Text.indd 7 14/08/09 8:50 AM phytoplankton

Zooplankton

baleen whales

sardines

sharks

whale shark

marlin the food web of the open ocean is complex. this simplified squid illustration shows just some of the ways in which the whole ecosystem is interdependent nutrients (upwelling) on its component parts.

8 environment, biology and fisheriesray’s bream

dead organic matter

FOTOO Offical Text.indd 8 14/08/09 8:50 AM Jellyfish

Zooplankton

sardines

dolphins marlin turtle sardines

sharks scads tuna

sunfish

sperm whales

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FOTOO Offical Text.indd 9 14/08/09 8:50 AM thesis. Nutrients are also necessary for their tens of millions, take their consider- As apex predators plant growth, which in the open ocean are able share, as do many species of seabird, of fish and squid, mainly derived from organic matter (dead each specialized in the size and type of dolphins and other animals and plants) formed by decompo- food they target. In fact, some species small, toothed sition on the ocean floor and brought to of seabird only eat small baitfish which whales consume the upper layers by upwelling currents. are driven to the surface by feeding tuna. large biomasses of The abundant phytoplankton form the Without the assistance of tuna, the birds smaller animals. vast pastures which are grazed upon by would have no source of food. marinethemes.com/ the zooplankton – tiny animals including Squid also feast on anchovies and David Fleetham the larval forms of many invertebrates, small fish, but they are also huge con- especially , and fishes. As well, sumers of zooplankton, particularly the the phytoplankton are the primary source teeming masses of tiny crustaceans which of food for the teeming schools of filter- form dense concentrations in the water feeding anchovies, herrings and pilchards, column (clearly visible at night on any not to mention probably the most abun- good depth sounder as this so-called scat- dant on earth, krill. tering layer rises to the surface). And of Oceanic food webs can be rather course, the many species of oceanic squid complicated. Small baitfishes such as themselves are a vital, often dominant anchovies, pilchards and sauries are the component of the diets of many animals staple diet of a whole array of larger ani- in different levels of the food web. Sperm mals, including many species of preda- whales, for example, eat squid almost tory fish. These include tuna, sharks, exclusively, while broadbill swordfish are dolphinfish, mackerel, wahoo, marlin, also particularly dependent on this abun- sailfish and swordfish. dant supply of protein. From the time they are only a few Other components of this tangled centimetres long, all of these species hunt web include marine turtles, which eat the seemingly defenceless baitfish schools. not only small fish, but also jellyfish and Other predators also take their turn to jellyfish-like such as salps. Then feast on this food supply. Dolphins and there are the mighty baleen whales which porpoises, which collectively number in filter great gulps of water through their

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FOTOO Offical Text.indd 10 14/08/09 8:50 AM The largest animals of the open ocean are all filter feeders. Here, humpback whales lunge upwards through schools of anchovies, taking huge mouthfuls of water which they strain through their baleen plates. seapics.com/ James Watt

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FOTOO Offical Text.indd 11 14/08/09 8:50 AM baleen, or ‘whalebone’ plates. In the As mentioned, sharks are important marine turtles Arctic and Antarctic, these whales graze components of the food web, consuming wander over vast easily on krill, while in more temperate small fi shes and squid in large quantities. distances of open waters they take advantage of concentra- But larger predatory sharks also prey on ocean consuming tions of baitfi shes. Witness the annual animals further up the web. As adults, small fish and appearance of dense schools of pilchards some, such as the white shark, become jellyfish along the off the South African and Western Aus- specialized feeders on marine mam- way. tralian coasts which are always attended mals, including seals, dolphins and even marinethemes.com/ by pods of hungry minke whales. whales. The tiger shark has evolved the David Fleetham On the subject of fi lter feeders, the singular ability to bite through marine largest fi shes on the planet, the basking turtle shells – a particular favorite food and whale sharks, also feed on the small- item of this widespread shark. Even at est organisms. Basking sharks do so by the apex of one part of the food web, the simply swimming through the plankton large marlins and tunas are targeted food with mouth agape, while whale sharks items for other predators, including large more actively suck in mouthfuls of water shortfi n mako sharks and one particular containing small crustaceans and school- species of toothed whale, the false killer ing fi sh, sometimes engulfi ng larger pred- whale. The latter appears to be a special- ators such as tuna in the process. ist predator of large oceanic fi shes, having

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FOTOO Offical Text.indd 12 14/08/09 8:50 AM Jellyfishes and other coelenterates are a significant proportion of macroplanktonic biomass and are eaten by a surprising variety of fishes and other marine animals. seapics.com/ Masa Ushioda

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FOTOO Offical Text.indd 13 14/08/09 8:50 AM a very wide gape and relatively large teeth will contain fi sh, or at least the remains compared with other toothed whales. of fi sh, sometimes, one species of fi sh completely dominating the diet. I well swimming the gauntlet remember the fi rst sailfi sh I dissected, One fascinating aspect of the oceanic the stomach of which was completely food web which makes it very different crammed with small pelagic toadfi sh. On from land-based food webs is the general other occasions, several different species principle of larger fi sh eating smaller fi sh of fi sh of different sizes might be found. regardless of species. Many land animals, For example, large blue marlin in Hawaii such as mammals and birds, produce are often found to contain very small large, well-developed young, and care for boxfi sh and triggerfi sh in their stomachs. them until they are virtually adult-sized Since marlin do not possess comb-like and have a good chance of survival. In the gill rakers which other species use to sift ocean, this is rarely the case. Most marine small food items from the water column, one of millions. fi sh produce millions of eggs each year, it would appear that large marlin pick off the developing which are simply released into the water, these tiny fi shes, one by one. egg of a fertilized and left at the mercies of the dolphinfish, currents. As each tiny larval fi sh grows breaking the web Coryphaena towards adulthood, it must run a perilous Marine ecosystems were in existence hippurus. many gauntlet. Baby tuna and marlin can and for hundreds of millions of years before open-ocean fishes will be eaten by any larger predatory fi sh, human predators began to take ever- produce huge including larger tuna and marlin. It is not increasing quantities of organisms from numbers of eggs uncommon to fi nd baby billfi sh inside different levels of the food web. Look- that float near the the stomachs of species like dolphinfi sh, ing at just some of the fi sheries of the surface, where while small marlin bills can often be open ocean which have developed only in they are fed upon found embedded in the stomach lining of the past few decades, annual catches of by other fishes adult marlin. The danger of being small several levels of food web animals have and specialist is probably why so many pelagic fi shes reached staggering levels. Global annual seabirds. have very rapid growth rates. ‘Grow or catches of skipjack tuna have recently Syd Kraul, Pacific die’ could well be the motto of the mixed topped two million tonnes, over half Planktonics layer. It is indeed a fi sh-eat-fi sh world. Those who fi sh can gain some idea of the food web immediately infl uencing their catch by conducting simple dietary studies on landed fi sh. Open the stom- ach of any pelagic fi sh and chances are you will fi nd a fairly broad range of food items. The main food groups you might expect to see would be crustaceans, mol- luscs and, of course, fi sh. The crustaceans might include the larvae of crabs (a very common dietary item of tuna and, some- times, marlin), free-swimming crabs, prawns, shrimps and, quite commonly, stomatopods – praying mantis-like creatures also known as prawn killers. Molluscs in the pelagic fi sh diet consist almost entirely of ; that is, squid, cuttlefi sh, octopuses (includ- ing paper nautilus and many species of pelagic octopus) and the occasional tiger nautilus. Often, the indigestible beaks of squid are all that remain of this very important group of prey. Most stomachs

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FOTOO Offical Text.indd 14 14/08/09 8:50 AM of which is taken in the western Pacifi c example, is there any discernible effect Ocean. More than one million tonnes of on prey species of removing large num- yellowfi n tuna are also removed annually bers of predatory fi shes such as tuna and from the world’s oceans, a high propor- billfi sh, or conversely, does the removal tion of the catch consisting of juvenile of many thousands of tonnes of baitfi sh, fi sh. Catches of sardines and squid would squid or krill have any effect on preda- each also top the million tonne mark, tors higher up the web? Other secondary while the take of smaller fi shes such as questions might include: Are these prey anchovies would be well over 10 million items, in terms of both species and size, tonnes. being actively selected, or is the feeding The Peruvian anchovy holds the of billfi shes and other predators prima- dubious distinction of being the most rily (or entirely) opportunistic? Is prey heavily exploited fi sh. The fi shery for (food) limiting at any stage of the life this tiny fi lter feeder, which was mainly cycle of predatory fi shes? Do popula- converted into dried fi shmeal, increased tions of predatory fi shes ‘boom or bust’ to a peak of over 13 million tonnes in depending on prey availability? What is 1971, but then almost completely col- the total biomass of predatory fi shes in lapsed and catches remained very low a given area at a given time, and what until the 1990s. The primary cause of the biomass of prey is required to sustain the collapse is now thought to be a strong El predator biomass? Niño event, but many also maintain that intensive fi shing must take at least some models of the oceanic ecosystem of the blame. Regardless of what or who Historically, fi sheries science has tended caused the demise of these baitfi sh, it was to be based on single species. For exam- clear that the animals which depended on ple, studies on striped bass, summer the baitfi sh, such as seabirds and larger fl ounder or skipjack tuna would concen- fi shes, were affected when their primary trate on considerations of the life cycle of food source diminished so dramatically. that particular species – its reproduction, The removal of such huge quanti- age and growth rates, and mortality rates ties of biomass from oceanic food webs (from natural causes and from fi shing) raises two very big questions: Are such being the primary concerns. Dietary stud- catches sustainable, and do they have any ies might be done also, but these would effect on the food webs themselves? For be secondary to the central study. Such

food items taken from the stomach of a juvenile longtail tuna, Thunnus tonggol. note the similar sizes of the organisms, including fish, crustaceans and squid, suggesting that the tuna has used its gill rakers to strain these items from the water column. Julian Pepperell

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FOTOO Offical Text.indd 15 14/08/09 8:51 AM an approach would result in a reasonable many species of oceanic squid. As the say- A feeding school understanding of the biology of a particu- ing goes, ‘garbage in, garbage out’, so with of skipjack tuna, lar species, but in isolation from the rest such major uncertainties about key ele- probably the most of its ecosystem. Studies might even have ments, these models as they stand may be prolific small included the effects of environmental interesting, but they are still some way off predator of the variables on the organism, such as tem- from being used as predictive tools in fish- open ocean perature or currents, but effects of or on eries management. What the models do Julian Pepperell other organisms were rarely considered show is that we need to know a lot more in detail. about the basic biology of many of the As our concept of ecosystems has building blocks of food webs. In fact, so improved, so too has the way in which little is known about the biology of many animals within an ecosystem are studied. of the building blocks of the oceanic food And with the great advances in comput- web that caution must be the primary con- ing power over the past several decades, cern in any development of any new fish- sophisticated ‘models’ of entire ecosys- ery within this complex system. tems, and therefore food webs, can now be generated. Competing with other predators Such models can be used, at least in One interesting argument has arisen from theory, to see what might happen if fish time to time to suggest that exploitation or other organisms are depleted at a given of fish and other organisms by humans trophic level. However, a major problem is not necessarily a major problem. This with such computer models is that they stems from the idea that all of the animals rely completely on the quality of the infor- which eat fish consume such huge quanti- mation fed into them. So, while we have ties that the human part of the equation fairly good information on the biology must be relatively minor. Such compari- and life cycles of some of the more com- sons suggest that quantities consumed by mercially important species, such as skip- seals, whales, dolphins and seabirds may jack and yellowfin tuna, little is known even be one or more orders of magnitude about critical parts of the food web, such greater than commercial (and recrea- as the biology of zooplankton, or of the tional) catches.

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FOTOO Offical Text.indd 16 14/08/09 8:51 AM While these arguments imply direct So, even though these sorts of sim- competition between humans and marine ple comparisons don’t tell us a lot about animals for the same resources, several direct competition between humans, important points need to be made. Com- fi shes and other marine animals, they do mercial and recreational catches con- help to focus on the connections between sist largely of finfish, while the diets of human use and the oceanic food web. We whales, dolphins and seabirds include know that at all levels within high proportions of cephalopods (squid the food web has existed in the oceans and octopus) and crustaceans. Seals for eons, and that such predation is the certainly target fish, some of which are cause of a large component of what is also caught by people, but they also called ‘natural mortality’ of fi shes and eat a lot of squid. As well, many of the other marine organisms. The very recent fishes being consumed by marine mam- introduction of the human element into mals and birds are not the same species ancient food webs is a new and poorly as those targeted by humans, or if they understood additional pressure on these are, they are not caught at the same natural systems and it is therefore risky sizes. Many of the most abundant spe- to increase exploitation on already exist- cies of seabirds, for example, eat very ing large scales before we have a fuller small fishes, or even fish eggs, while it is understanding of the whole picture. We also known that whales rarely compete can coexist with and within these food directly with humans for the same fish webs. We just have to learn more, and stocks. take care at every step along the way.

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FOTOO Offical Text.indd 36 14/08/09 8:53 AM guide Partto the fishes two

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FOTOO Offical Text.indd 37 14/08/09 8:53 AM 5 Billfishesbillfishes

FOTOO Offical Text.indd 38 14/08/09 8:53 AM blue marlin he blue marlin is a true giant of the mum body depth), its folding pectoral ocean. its confirmed maximum size of fi ns and its proportionally large fi rst anal nigricans t BB 820 kg (1805 lb) makes it the second largest fi n. Other features are its relatively short teleost (bony) fish, after the oceanic sunfish, lower jaw, and its gunmetal blue-gray OTHER COMMON NAMES france marlin bleu Mola mola. blue marlin occur in all three of color after death. A further feature to hawaii a’u the world’s major oceans. the indo-pacific separate blue marlin from black marlin is Japan Kurokajiki populations have always been regarded that in the blue, the second dorsal fi n is spain marlin azul as a single species, but blue marlin of the anterior to the second anal fi n, whereas in aguja azul atlantic and the indo-pacific have long been the black marlin, the relative fi n positions considered by some scientists to be separate are the other way round. species – Makaira nigricans in the atlantic The distribution of blue marlin is and Makaira mazara in the indo-pacific. the circumtropical, extending in summer to only feature described as different between about 45° latitude in both hemispheres. the two is the pattern of the lateral line. on Blue marlin are the most tropical of the the surface, the lateral line of blue marlin is istiophorid billfi shes, as well as the most virtually invisible, but forms a ‘chicken-wire’ oceanic. They are normally found near like pattern on the underside of the skin, the islands or in the open ocean throughout ‘mesh’ of which is smaller in atlantic fish their range, not usually being strongly compared with those from the indo-pacific. associated with continental shelves (as is however, more recent genetic studies indi- the black marlin). cate that these differences are insufficient The main recreational fi shing areas to warrant their separation into separate for blue marlin around the world tend to species. be near islands. These include Hawaii in The blue marlin can be identifi ed by the Pacifi c, Mauritius in the Indian, the its relatively high, pointed fi rst dorsal Caribbean islands in the Atlantic as well fi n (usually about two-thirds the maxi- as many smaller islands in each ocean.

M

Billfishes F

billfishes 39

FOTOO Offical Text.indd 39 14/08/09 8:53 AM These islands are all tropical to subtropi- tius in the – the first proven Above This shot of cal, and appear to be locations of sea- movement between two oceans for any a large blue marlin sonal spawning for blue marlin. billfish (Atlantic to Indian). epitomizes the Hawaii and Mauritius are well- In the Pacific, tagging of blue mar- power and beauty known ‘hot spots’ for the occurrence of lin off southwestern United States and of this extraordinary large, probably spawning female blue Hawaii has revealed some very extensive fish. marlin, but in the Atlantic, relatively few movements as well. The most notable of Guy Harvey very large – 454 kg (1000 lb) plus – speci- these was a blue marlin tagged off Hawaii mens had been recorded until the 1990s. that was recaptured near Taiwan. Off Below A rare photo However, within several years of the dis- Australia, even though over 5000 blue of a large blue covery of large blue marlin around the marlin have been tagged and released, marlin underwater, island of Madeira, more thousand-pound there have only been 17 recaptures to taken near the blue marlin had been caught from those date. Again, however, one of these was island of Madeira. waters than had been taken during the highly noteworthy. This was a blue mar- Note in particular long history of game fishing in the entire lin tagged off the Australian southeast the high dorsal and Atlantic Ocean. These fish were found to coast, and recaptured 18 months later by anal fins. be not in spawning condition, and over a Japanese longliner 300 nautical miles Guy Harvey time, their occurrence near Madeira has south of Sri Lanka – the second interoce- proven to be as enigmatic as it is unpre- anic movement of a (Pacific to dictable. Indian) and again, a blue marlin. The majority of blue marlin have The two largest billfish ever weighed been tagged by recreational anglers in the and verified, both caught off Hawaii, were Atlantic Ocean, mainly from the eastern blue marlin. The largest weighed 820 kg United States and in the Caribbean. Over (1805 lb) and was landed by a party of 30 years, tens of thousands of blue marlin novice anglers aboard a charter boat off have been tagged in the region, and hun- Honolulu in 1971. The second heaviest dreds recaptured. Movements of tagged billfish weighed 753 kg (1656 lb) and was fish have been extensive, with several caught off Kona, Hawaii, in 1984. There transatlantic crossings being recorded. are many anecdotal reports of blue mar- The most startling recapture, however, lin weighing in excess of 2000 lb (909 kg) was a fish tagged off South Carolina and – even as high as 2600 lb (1180 kg) – recaptured three years later near Mauri- being caught by commercial longline ves-

40 guide to the fishes

FOTOO Offical Text.indd 40 14/08/09 8:54 AM sels, but it is not possible to verify any of simply be because they don’t stay small Above a typical these accounts. for very long. small blue marlin There have been several studies of According to early Japanese studies, leaps in the calm the growth rates of blue marlin, based on blue marlin apparently have extensive waters of new examination of their bony parts, in par- spawning areas throughout the tropical britain, off the ticular, fi n spines and otoliths (ear bones). and subtropical Pacifi c, Indian and Atlan- coast of papua These studies have tended to assume that tic oceans. This picture is based almost new guinea. the rings or other regular marks each repre- entirely on the occurrence of larval blue blue marlin is the sent one year of growth, but this has not marlin over very broad areas of these dominant billfish been verifi ed for blue marlin. One study three oceans, and also assumes that bill- species around which assumed annual growth rings esti- fi sh larvae have been correctly identifi ed tropical islands. mated a 70 kg (154 lb) male blue marlin in these surveys. Julian Pepperell to be six years old; however, if blue mar- Spawning adult blue marlin do lin grow at a similar rate to black marlin appear to be patchily distributed, and are Below illustrations (and they may not), then a fi sh of this size mainly found in seasonal aggregations of larval blue would only be about two to three years around isolated islands. Around Hawaii, marlin. while old. it has been found that nearly 80 per cent all other billfish By examining what are assumed of the blue marlin landed during summer develop their bills to be daily growth rings on otoliths of are males, mostly less than about 90 kg very early, blue very small fi sh, the early growth rate (200 lb) in size. Female fi sh caught at marlin lack a bill of blue marlin does appear to be very the same time cover a much greater size until they attain a rapid, reaching 30 kg (66 lb) within the range, from as small as 22 kg (48 lb) to length of about fi rst year. It is theorized that all of the over 600 kg (1320 lb). Examination of 1 metre. billfi shes initially grow in length very the gonads of these fi sh has shown that From Gehringer, JW quickly, presumably in order to be able spawning of blue marlin, at least at the (1956), Fisheries to outswim predators as soon as possible. latitude of Hawaii, is highly seasonal and Bulletin (US) 57: This is also an explanation for why very predictable. Similar results have been 123–132. small billfi sh are rarely caught – it may obtained at Mauritius, indicating that

billfishes 41

FOTOO Offical Text.indd 41 14/08/09 8:54 AM two decades. In the next study, six blue marlin, all caught by rod and reel, were tracked off Kona, Hawaii, for up to 48 hours. For the fi rst few hours after release, vertical movements were somewhat erratic; however, fi sh then tended to settle into relatively predictable behavior pat- terns. Cruising speed averaged about two knots, and the great majority of time was spent within the so-called ‘mixed layer’ to a depth of about 80 metres, the level of the thermocline. Thus, vertical movements of the marlin oscillated between the sur- face and the thermocline, with occasional brief forays into colder, deeper water. This was the fi rst proof of the highly surface- oriented behavior of any marlin species, and has proven to be very important in understanding catch rates by commercial longlining fl eets using hooks which are set a blue marlin blue marlin are apparently able to locate above and below the thermocline. about to be remote islands as the spawning season Perhaps the most interesting fi nding released off the approaches. which emerged from this, and subsequent pacific coast of A 400 kg (880 lb) blue marlin may work using more sophisticated electronic guatemala, after produce as many as 150 million eggs, tags, is that the depth at which blue mar- being tagged each a little over 1 mm in diameter. As is lin swim is strongly infl uenced by time of with a popup the case for other billfi shes, fertilization day. During daylight hours, fi sh tend to satellite tag is external, and hatching of the tiny lar- swim deeper, often near the thermocline, Julian Pepperell vae occurs at the surface within two days. whereas at sunset, behavior changes and One recent study suggests that female they become much more surface-oriented blue marlin (as well as sailfi sh and white during the night. What is unknown at marlin) may spawn as many as four times this stage is whether feeding still takes in one season, but it is also speculated place at night. Use of popup satellite that spawning frequency may be much tags over much longer periods showed higher. that vertical behavior remains relatively As blue marlin larvae grow, they dif- predictable. There is a tendency for fi sh fer from all other billfi shes in that they do to keep moving away from their release not develop a bill until they reach quite a points, but parallel to the coast, through- large size – over 5 kg (11 lb) and 1 metre out the tracking periods, one fi sh moving in length. This feature suggests that all of over 160 km away from its release point the other billfi shes (broadbill excluded) in four days. form a relatively closely related group, Like most of the other istiophorid with blue marlin representing an offshoot billfi shes, the blue marlin is an inciden- or outlier species. tal bycatch of the tuna longline fl eets of The fi rst attempts to track billfi sh the world. In addition, signifi cant num- after release, using a tag which emitted bers are also taken as a bycatch of purse sonic pulses, were carried out on blue seine vessels which set their nets around marlin off Hawaii in the early 1970s. fl oating logs. Stock assessment studies in Equipment failure and shark attack took the Atlantic Ocean strongly point to over- their toll, but several successful tracks exploitation of blue marlin in that region, were obtained, paving the way for the but in the Pacifi c, it appears that blue more sophisticated technology of the next marlin stocks may be stable.

42 guide to the fishes

FOTOO Offical Text.indd 42 14/08/09 8:54 AM blacK marlin BBIstiompax indica OTHER COMMON NAMES france marlin noir hawaii silver marlin Japan shirokajiki M spain aguja negra eastern pacific black marlin

F black marlin

M black marlin

he black marlin is the least common of only istiophorid in which the second dor- tthe world’s four species of marlin and, as sal fi n is anterior to the second anal fi n – a result, is one of the least studied and least a feature which holds for all sizes. Lastly, understood of the billfishes. this is one of the dorsal fi n of the black marlin is the the largest of the teleost (bony) fishes in the lowest of all of the istiophorids, measur- world, growing to over 4 metres in length ing no more than half the maximum body and up to 709 kg (1560 lb) in weight. depth in adults. The main feature which sets the black Although black marlin are distrib- marlin apart from all other billfi shes is its uted throughout the Indo-Pacifi c between rigid pectoral fi ns. In adults, these fi ns about latitudes 40°N and 40°S, closer cannot be folded against the body, even examination of historic Japanese catch with reasonable force. It should be noted, rates clearly shows that the density of the however, that very small fi sh have fl ex- species is very sparse in open-ocean areas, ible pectoral fi ns, the calcifi cation of the but much more ‘clumped’ near large land pectoral joint which causes this rigidity masses and continents. In fact, the black not occurring until a size of about 10 to marlin is the most land-associated of the 15 kg (20 to 30 lb). Another diagnostic billfi shes, preferring waters on or near feature is the position of the second dor- continental shelves during most stages of sal and anal fi ns. The black marlin is the its life cycle.

billfishes 43

FOTOO Offical Text.indd 43 14/08/09 8:54 AM Areas where black marlin aggregate Brazil and even in the Caribbean. The Above a black include the northern part of the Great likely route for these infrequent ‘inva- marlin shows its Barrier Reef, the east coast and the north- sions’ would be around the Cape of Good speed and power west shelf of Australia, extending to the Hope, and most world distribution maps before being southern islands of Indonesia, the South of black marlin show dotted arrows fol- brought to the China Sea off Vietnam, Malaysia and lowing this route. Even so, such occur- boat and tagged. Thailand, in the eastern Pacifi c off Peru rences are considered very rare. boyceimage.com and Central America (Panama and Ecua- Most tagging of black marlin by rec- dor) and off Kenya and Mauritius in the reational anglers has been undertaken off Below left Indian Ocean. eastern Australia. The fi rst black marlin a beautiful baby Black marlin do not occur in the was tagged off Cairns, Australia, in 1968 black marlin Atlantic Ocean; however, Japanese and since then, more than 46 000 black caught and research longliners historically recorded marlin have been tagged off eastern Aus- released off stray black marlin from time to time in tralia. Of the total tagged, more than 350 southeastern the Atlantic as far north as the coast of recaptures have been recorded, adding australia. note the extremely high , typical of all very young billfish. Tom Buxton

44 guide to the fishes

FOTOO Offical Text.indd 44 14/08/09 8:54 AM substantially to our knowledge of this with time at liberty, at least for the first An adult species. nine months or so after release. This rapid black marlin The long-distance movements of dispersal takes fish away from the tagging photographed some tagged fish give the impression of grounds off eastern Australia throughout off the Great mass long-distance dispersal of black the western Pacific and beyond at an Barrier Reef, marlin. However, this picture does not average rate of approximately 20 km per Australia. Note necessarily mean that many or most fish day. (Minimum movement rates of over the rigid, curved take these routes in all or most years. 60 km per day have been recorded for pectoral fin and It does, however, clearly indicate that some recaptured fish, but these have been the relatively low the species is capable of very extensive short-term recaptures and are the excep- dorsal fins, both movements and that exchange of indi- tion to the rule.) In addition, the recap- characteristics of viduals throughout the species’ Pacific- ture data also show that there is a very this species. wide range can and does occur. A study marked ‘cluster’ of recaptures near the Guy Harvey of the genetics of black marlin in the point(s) of release after about one year Indo-Pacific confirmed this picture in that (330 to 400 days) followed by another no differences could be found between period of apparent rapid dispersal in the DNA ‘fingerprints’ from fish taken from ensuing months. Clustering of recaptures throughout the black marlin’s range. This near release points is also apparent after finding of apparent widespread mixing two years, and also after three, four and indicates that there is almost certainly five years (with decreasing numbers of only one stock of black marlin in the recaptures as time increases). This fasci- Pacific (quite possibly extending to the nating finding suggests either that some Indian Ocean as well). The important fish never leave the areas in which they implication of this finding is that interna- were tagged, or that annual homing tional cooperation in managing the spe- occurs, at least for a proportion of the cies needs to be on an ocean-wide scale. population. Careful examination of Japa- Another question raised by the tag- nese catch data for the Great Barrier Reef ging results is whether the movements of over long periods showed that, by early black marlin are random, or part of some summer each year, catch rates of black purpose-driven migratory cycle. Tagging marlin suddenly declined dramatically, results clearly show that, after a period indicating a sudden en masse departure of several months, the average distance of fish from that area over a very short moved by tagged fish increases rapidly time. Long-term charter boat captains in

billfishes 45

FOTOO Offical Text.indd 45 14/08/09 8:55 AM the area also attest to the fact that black a 100 kg (220 lb) fish would be three to This black marlin, marlin virtually disappear completely at four years old. A small sample of very estimated at this time, leading to the conclusion from small black marlin have been aged by about 10 kg tag returns that at least some fish must be counting presumed daily rings on their (22 lb) in weight, returning to the reef on an annual basis. otoliths. Previous work on tuna indicates would be less than An important question is, what propor- that these rings are laid down every day one year old. tion of the population completes this during the early life of fish, and assuming Peter Bristow annual cycle? Perhaps the next genera- that this is also the case for marlin, two tion of high-tech satellite tags will pro- 4 kg (9 lb) black marlin were estimated vide the answer. to have been only about 130 days (four By analyzing the size ‘pulses’ of months) old when they were caught. A small black marlin which appear along rare, even smaller specimen of a black the east coast of Australia, it has been marlin, only 45 cm in length, was also estimated that they reach a size of about aged in this way and estimated to be 25 kg (55 lb) at one year of age, and that about 80 days old. After several years of age, the growth rates of black marlin become more dif- ficult to assess, but all evidence so far points to continued rapid growth. It is quite likely (but as yet, unproven) that male black marlin grow more slowly than females and die at an earlier age, explaining why all fish over about 170 kg (375 lb) are females. The maximum size to which black marlin grow is of the order of 700 kg (1540 lb), the all-tackle world record for the species being 708 kg (1560 lb) for a fish caught off Peru in 1953, while another weighing 691.7 kg (1525 lb) was caught in the same area in 1954. Nearly 600 fish weighing more than 454 kg (1000 lb) have been captured since then, nearly all off Cairns, Australia, but none has exceeded these two long-standing records. There are persistent anecdotes of much larger black marlin being caught by longline vessels, but none of these has ever been substantiated. Examining the gonads of black mar- lin caught by both recreational anglers and Japanese longliners, together with some records of occurrence of black mar- lin larvae, has revealed that spawning takes place in the Coral Sea in late spring/ early summer each year. Egg counts from ovaries taken from adult females weigh- ing between 400 kg (880 lb) and 600 kg (1320 lb) ranged from 65 million to 250 million eggs. As is the case for other istio- phorids, the frequency of spawning for black marlin is not known. The fully ripe eggs of the black mar- lin, about 1.3 mm in diameter, are fer-

46 guide to the fishes

FOTOO Offical Text.indd 46 14/08/09 8:55 AM tilized externally, after which they fl oat recorded have only been to about 180 at the surface for several days before metres. During tracking, fi sh tended to hatching into tiny larvae. The larvae are initially move offshore from the edge of themselves miniature predators of the reefs before heading parallel to the shore. planktonic world – all eyes and mouth, The average mean swimming speeds over with one purpose – to eat and, therefore, the ground for tracks lasting up to 28 to grow. The mortality rate during these hours ranged from about 1.5 to 4 knots. critical early stages must be prodigious, Although black marlin are not now as a whole suite of slightly larger preda- targeted by most commercial fi sheries in tors take their relentless toll. Although the Pacifi c, the numbers taken each year mortality rates are obviously extremely as bycatch are quite large. It has been high, it is still diffi cult to understand why estimated that in the western and cen- very small black marlin, less than about tral Pacifi c, at least 30 000 black mar- 10 kg (22 lb), are extremely rare in recre- lin are taken annually. Beginning in the ational and commercial catches. It is pos- early 1950s, Japanese longliners consist- sible that, during this phase of their life ently fi shed off northern Queensland, cycle, very small fi sh remain offshore in Australia, and during the peak years of the midwater zone, and are therefore not the 1960s, up to 14 000 fi sh were taken available to most fi shing gears, although annually by that fi shery. A long-standing this explanation obviously needs to be charter fi shery for black marlin off the tested. Great Barrier Reef, Australia, has oper- The vertical behavior of black marlin ated successfully for more than 40 years. has been revealed by tracking using ultra- During that time, strike rates have fl uc- sonic tags, as well as by analyzing data tuated considerably, but the fi shery has from popup satellite tags. In most cases, proven itself to be sustainable over this tagged black marlin tended to swim entire period. Black marlin are also a sig- closer to the surface during the night nifi cant component of a recreational fi sh- compared with the day. There is also a ery off Panama. In the 1950s, many large tendency for fi sh to dive to deeper depths black marlin, including the two largest on after dawn, and to make more ascents to record, were caught by a small group of the surface after about noon. Tagged fi sh anglers operating from a fi shing lodge in rarely penetrated the thermocline, and Peru. The question of whether or not that then only briefl y, remaining at tempera- area still attracts and holds a population tures no more than 8°C below that of the of black marlin is one which many would surface waters. The deepest dives so far like to answer.

billfishes 47

FOTOO Offical Text.indd 47 14/08/09 8:55 AM While these arguments imply direct So, even though these sorts of sim- competition between humans and marine ple comparisons don’t tell us a lot about animals for the same resources, several direct competition between humans, important points need to be made. Com- fi shes and other marine animals, they do mercial and recreational catches con- help to focus on the connections between sist largely of finfish, while the diets of human use and the oceanic food web. We whales, dolphins and seabirds include know that predation at all levels within high proportions of cephalopods (squid the food web has existed in the oceans and octopus) and crustaceans. Seals for eons, and that such predation is the certainly target fish, some of which are cause of a large component of what is also caught by people, but they also called ‘natural mortality’ of fi shes and eat a lot of squid. As well, many of the other marine organisms. The very recent fishes being consumed by marine mam- introduction of the human element into mals and birds are not the same species ancient food webs is a new and poorly as those targeted by humans, or if they understood additional pressure on these are, they are not caught at the same natural systems and it is therefore risky sizes. Many of the most abundant spe- to increase exploitation on already exist- cies of seabirds, for example, eat very ing large scales before we have a fuller small fishes, or even fish eggs, while it is understanding of the whole picture. We also known that whales rarely compete can coexist with and within these food directly with humans for the same fish webs. We just have to learn more, and stocks. take care at every step along the way.

the oceanic web of life 17

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