Effect of Light on Juvenile Walleye Pollock Shoaling and Their Interaction with Predators

Total Page:16

File Type:pdf, Size:1020Kb

Effect of Light on Juvenile Walleye Pollock Shoaling and Their Interaction with Predators MARINE ECOLOGY PROGRESS SERIES Vol. 167: 215-226, 1998 Published June 18 Mar Ecol Prog Ser l Effect of light on juvenile walleye pollock shoaling and their interaction with predators Clifford H. Ryer*, Bori L. Olla Fisheries Behavioral Ecology Group, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Hatfield Marine Science Center, Newport, Oregon 97365, USA ABSTRACT: Research was undertaken to examine the influence of light lntenslty on the shoaling behavior, activity and anti-predator behavior of juvenlle walleye pollock Theragra chalcogramrna. Under a 12 h light/l2 h dark photoperiod, juveniles displayed a diurnal shoaling and activity pattern, characterized by fish swimming in cohesive groups during the day, with a cessation of shoaling and decreased swlmmlng speeds at nlght. Prior studies of school~ngfishes have demonstrated distinct light thresholds below which school~ngabruptly ceases. To see if this threshold effect occurs in a predomi- nantly shoaling species, like juvenile walleye pollock, another experiment was undertaken in which illumination was lourered by orders of magnitude, glrrlng fish 20 mln to adapt to each light intensity Juvenlle walleye pollock were not characterized by a d~stinctlight threshold for shoaling; groups grad- ually dispersed as light levels decreased and gradually recoalesced as light levels increased. At light levels below 2.8 X 10.~pE SS' m-" juvenile walleye pollock were so dispersed as to no longer constitute a shoal. Exposure to simulated predation risk had differing effects upon fish behavior under light and dark cond~tionsBrief exposure to a mndc! prerlst~r:E !he .'ark c;i;ssd fish to ~WIIIIidsier, ior 5 or 6 min, than fish which had been similarly startled In the light. Chronic exposure to a l~vingpredator produced simllar results; fish tended to swlm slower when a predator was present in the light, but faster when a predator was present in the dark. In the light, shoallng and/or school~ngprovide protection against predators. But in the dark, with f~shunable to see one another, increased prey activlty resulting from predator disturbance may lead to accelerated dispersal of prey shoals Thus, perceived predation risk may have different effects upon the spatial d~stnbutionof luvenlle walleye pollock under light and dark conditions. This has implications for surv~val,as f~shwh~ch have become widely scattered durlng the darkness may take longer to reform shoals at dawn, resulting in greater predation nsk. KEY WORDS Schooling Spat~aldistnbut~on Tw~lighthypothesis Predator-prey Swimming speed Illumination INTRODUCTION dividuals within a school (Partridge & Pitcher 19801, it is unlikely that in the wild many species are capable of The means by which fish forin and maintain shoals schooling in the absence of sufficient light. Thls impres- and schools has long been of interest to fisheries scien- sion is supported by observational (Emery 1973, Helf- tists and behavioral ecologists. Since the early investi- man 1979) and bioacoustical studies which generally gations of schooling, it has been evident that the show that shoals and schools disperse at night (Appen- amount of light reaching the fish's eye largely deter- zeller & Leggett 1992, Brodeur & Wilson 1996). Since mines whether or not it is able to school (Breder 1951, ambient light in marine and aquatic habitats may vary Atz 1953, Shaw 1961, Hunter 1968). Although other greatly according to depth, turbidity, season, lunar senses, such as the lateral line system, may play an im- stage and cloud cover (McFarland 1986), the meaning portant role in the spatial and angular orientation of in- of 'night', relative to light levels, 1s rather ambiguous. Numerous studies have been directed towards deter- mining the relationship between light intensity and some measure of the ability or inclination of fish to form O Inter-Research 1998 Resale offull article not pei-n~itted 216 Mar Ecol Prog Ser 167: 215-226, 1998 cohesive groups. In some species there is a gradual de- In this paper we examine the influence of light on the crease in schooling or shoaling as light levels decrease shoaling and anti-predator behavior of juvenile wall- (John 1964), while for others, there is a threshold light eye pollock Theragra chalcogramma. The walleye pol- level at which this behavior abruptly ceases. This lock is a pelagic species of the northern Pacific Ocean threshold varies from 3.7 X 10-2 pE S-' m-* for the which supports a large commercial fishery and, in its Hawaiian silverside Pranesus insularurn (Major 1977) juvenile phase, is preyed upon by numerous species of to 1.8 X lO-? pE S-' m-2 for the Atlantic mackerel groundfish, birds and marine mammals (Livingston Scomber scombrus (Glass et al. 1986), with most other 1993).For juveniles, gregarious behavior typically con- species examined falling somewhere between these sists of shoaling (Pitcher 1980), with fish forming extremes (Higgs & Fuiman 1996).Putting this in an eco- loosely structured groups (Ryer & Olla 1995).Juveniles logical context, Glass et al. (1986) concluded that At- will form more highly structured schools (Pitcher lantic mackerel should be able to school to depths of 1980),but only when they are rapidly moving from one 20 m on clear starlit nights and perhaps to 80 or 100 m location to another. In the Bering Sea, juvenile walleye on clear moonlit nights, whereas cloud cover could pollock have been reported to exhibit a diel pattern of make schooling at night impossible, even at the surface. vertical migration, moving upwards into surface wa- One of the well-established functions of gregarious ters during dusk, followed by a return to depth around behavior, e.g. shoaling, schooling, flocking and herd- dawn (Bailey 1989, Tang et al. 1996). In the western ing, is to facilitate the individual's ability to detect and Gulf of Alaska, Brodeur & Wilson (1996) observed a mitigate predatory threat (Lazarus 1979). Individuals similar diel migration, but also reported that juveniles in groups are likely to detect predators at greater dis- formed highly cohesive aggregations near the bottom tances (Magurran et al. 1985) and are often less vul- during the day and dispersed in the surface waters nerable due to coordinated escape responses (Pitcher during the night. Without knowledge of the in situ light & Parrish 1993) which result in predator confusion levels and light thresholds for shoaling behavior, it is (Neill & Cullen 1974, Landeau & Terborgh 1986) as impossible to know whether such dispersive behavior well as dilutiodattack abatement effects (Bertram results from fish actively leaving social groups to indi- 1978, Turner & Pitcher 1986).Attacks by predators are vidually seek out prey (Ryer & Olla 1995), or from the frequently concentrated during twilight periods (Major inability of fish to maintain shoals at the ambient light 1977, Parrish 1992),when prey are silhouetted against levels involved. A prior laboratory study demonstrated the downwelling light from the surface and predators that juvenile walleye pollock shoals become less cohe- approaching from below are difficult for prey to detect sive at night (Sogard & Olla 1996). But, this study uti- against the darkness of the depths (Munz & McFarland lized a night-time light level of 0.1 pE S-' m-', which is 1973). Yet, little is known about how predators and more typical of twilight than night-time, leaving open prey interact in darkness and how this will influence the question of how lower light levels influence shoal- the spatial distribution of prey. With their dependence ing. Beyond its interest from a purely ecological per- upon vision, it is clearly not feasible for most shoaling spective, knowledge of distribution patterns in juve- and schooling species to maintain, much less form, nile shoaling and schooling fishes, and the underlying more cohesive groups in the dark. However, fish may mechanisms which produce them, may aid in design- have evolved other behaviors that minimize their noc- ing the sampling protocols needed to predict future turnal vulnerability and perhaps facilitate the reforma- abundance of these species (Neilson & Perry 1990). tion of groups at dawn. Some fish species decrease To address the relationship between light and shoal- their activity during the night (Emery 1973, Helfman ing in juvenile walleye pollock, we examined the 1993) to conserve energy and possibly to reduce con- shoaling intensity and swimming speeds of juvenile spicuousness to predators. For shoaling and schooling walleye pollock over 2 consecutive days under a 12 h fish, this may also minimize group dispersal and light/l2 h dark photoperiod, to elucidate diel patterns decrease the time required for individuals to locate of behavior in the laboratory. Next, we conducted an conspecifics and reform shoals or schools at dawn. Sev- experiment to see if there is a distinct threshold light eral stud.ies have shown that, with the onset of morning level at which shoaling ceases, decreasing illumination twilight, fish begin forming groups before they com- from 3.9 pE S-' m-2 to darkness in incremental order of mence other activities such as feeding (Helfman 1979, magnitude steps, and then incrementally increasing Pitcher & Turner 1986). Since twilight is a period of light back to the 3.9 pE S-' m-2 level. At each level we intense predation, any influence that predators have monitored shoal behavior and activity. upon the dispersal of prey during the darkness, If the dispersal of juvenile walleye pollock in dark- thereby influencing the speed of group reforma.tion at ness results from an inability to shoal, the rate of dis- dawn, should influence individual vulnerability to pre- persal may be influenced by any factor which affects dation at dawn. fish activity. When there is adequate light for shoaling, Ryer & Olla: Light, predat~onand shoaling In a pelagic fish the presence of predators has been shown to decrease CCD Camera - juvenile walleye pollock swimming speeds (Ryer & Incandescenl Olla 1997).However, in preliminary experiments we ,tighk , noted that juvenile walleye pollock startled by human k activity in the darkness tended to become agitated and more active than juveniles startled in the light.
Recommended publications
  • Pacific Herring
    THE MULTITUDINOUS PACIFIC HERRING by D. N. OUTRAM FISHERIES RESEARCH BOARD OF CANADA BIOLOGICAL STATION, NANAIMO, B. C. CIRCULAR NO. 6 3^*u DECEMBER, 1961 COVER PHOTOGRAPH: A mountain of herring covers the storage bin area of the reduction plant at Imperial Cannery, Steveston, B„ C„, awaiting processing into fish meal and oil. Photographs by Mr. C. Morley. THE MULTITUDINOUS PACIFIC HERRING . Vast Shoals of Protein-Rich Herring Rove the Temperate Coastal Waters Along Canada's Western Seabord N V By Donald N, Outram y ^v- _•• HISTORICAL BACKGROUND annually. While this fishery is. Fabulous numbers of herring first in landed weight and second (Fig. l) are found along the sea- to salmon in landed value, it is washed shores of Canada's most wes only worth about one-quarter as much terly province, Their migrations, as the salmon catch. their sudden abundance and their Fluctuations in the world price straggle to survive is an exciting of fish meal and oil cause the market study. Undoubtedly, herring were one value at about ten million dollars to of the first coastal fishes to be vary from year to year, utilized by man. In northern Europe, FISHING FOR HERRING particularly, they have been a source The British Columbia herring of food since before written history. fishery is a highly organized opera Herring and herring roe have been an tion utilizing modern shore plants and article of food or barter of the efficient fishing vessels . The seventy- coastal Indian tribes of British Col to eighty-foot long seine boats are umbia for ma.ny centuries, They were equipped with the very latest electronic not fished, however, on a commercial fish-detecting equipment, enabling the basis until 1877 when 75 tons were fishermen to "see" the shoals before caught.
    [Show full text]
  • SUSTAINABLE FISHERIES and RESPONSIBLE AQUACULTURE: a Guide for USAID Staff and Partners
    SUSTAINABLE FISHERIES AND RESPONSIBLE AQUACULTURE: A Guide for USAID Staff and Partners June 2013 ABOUT THIS GUIDE GOAL This guide provides basic information on how to design programs to reform capture fisheries (also referred to as “wild” fisheries) and aquaculture sectors to ensure sound and effective development, environmental sustainability, economic profitability, and social responsibility. To achieve these objectives, this document focuses on ways to reduce the threats to biodiversity and ecosystem productivity through improved governance and more integrated planning and management practices. In the face of food insecurity, global climate change, and increasing population pressures, it is imperative that development programs help to maintain ecosystem resilience and the multiple goods and services that ecosystems provide. Conserving biodiversity and ecosystem functions are central to maintaining ecosystem integrity, health, and productivity. The intent of the guide is not to suggest that fisheries and aquaculture are interchangeable: these sectors are unique although linked. The world cannot afford to neglect global fisheries and expect aquaculture to fill that void. Global food security will not be achievable without reversing the decline of fisheries, restoring fisheries productivity, and moving towards more environmentally friendly and responsible aquaculture. There is a need for reform in both fisheries and aquaculture to reduce their environmental and social impacts. USAID’s experience has shown that well-designed programs can reform capture fisheries management, reducing threats to biodiversity while leading to increased productivity, incomes, and livelihoods. Agency programs have focused on an ecosystem-based approach to management in conjunction with improved governance, secure tenure and access to resources, and the application of modern management practices.
    [Show full text]
  • Dispersal, Philopatry, and the Role of Fissionfusion Dynamics In
    MARINE MAMMAL SCIENCE, **(*): ***–*** (*** 2012) C 2012 by the Society for Marine Mammalogy DOI: 10.1111/j.1748-7692.2011.00559.x Dispersal, philopatry, and the role of fission-fusion dynamics in bottlenose dolphins YI-JIUN JEAN TSAI and JANET MANN,1 Reiss Science Building, Rm 406, Department of Biology, Georgetown University, Washington, DC 20057, U.S.A. ABSTRACT In this quantitative study of locational and social dispersal at the individual level, we show that bottlenose dolphins (Tursiops sp.) continued to use their na- tal home ranges well into adulthood. Despite substantial home range overlap, mother–offspring associations decreased after weaning, particularly for sons. These data provide strong evidence for bisexual locational philopatry and mother–son avoidance in bottlenose dolphins. While bisexual locational philopatry offers the benefits of familiar social networks and foraging habitats, the costs of philopatry may be mitigated by reduced mother–offspring association, in which the risk of mother–daughter resource competition and mother–son mating is reduced. Our study highlights the advantages of high fission–fusion dynamics and longitudinal studies, and emphasizes the need for clarity when describing dispersal in this and other species. Key words: bottlenose dolphin, Tursiops sp., association, juvenile, philopatry, locational dispersal, mother-offspring, ranging, site fidelity, social dispersal. Dispersal is a key life history process that affects population demography, spatial distribution, and genetic structure, as well as individual
    [Show full text]
  • Disease List for Aquaculture Health Certificate
    Quarantine Standard for Designated Species of Imported/Exported Aquatic Animals [Attached Table] 4. Listed Diseases & Quarantine Standard for Designated Species Listed disease designated species standard Common name Disease Pathogen 1. Epizootic haematopoietic Epizootic Perca fluviatilis Redfin perch necrosis(EHN) haematopoietic Oncorhynchus mykiss Rainbow trout necrosis virus(EHNV) Macquaria australasica Macquarie perch Bidyanus bidyanus Silver perch Gambusia affinis Mosquito fish Galaxias olidus Mountain galaxias Negative Maccullochella peelii Murray cod Salmo salar Atlantic salmon Ameirus melas Black bullhead Esox lucius Pike 2. Spring viraemia of Spring viraemia of Cyprinus carpio Common carp carp, (SVC) carp virus(SVCV) Grass carp, Ctenopharyngodon idella white amur Hypophthalmichthys molitrix Silver carp Hypophthalmichthys nobilis Bighead carp Carassius carassius Crucian carp Carassius auratus Goldfish Tinca tinca Tench Sheatfish, Silurus glanis European catfish, wels Negative Leuciscus idus Orfe Rutilus rutilus Roach Danio rerio Zebrafish Esox lucius Northern pike Poecilia reticulata Guppy Lepomis gibbosus Pumpkinseed Oncorhynchus mykiss Rainbow trout Abramis brama Freshwater bream Notemigonus cysoleucas Golden shiner 3.Viral haemorrhagic Viral haemorrhagic Oncorhynchus spp. Pacific salmon septicaemia(VHS) septicaemia Oncorhynchus mykiss Rainbow trout virus(VHSV) Gadus macrocephalus Pacific cod Aulorhynchus flavidus Tubesnout Cymatogaster aggregata Shiner perch Ammodytes hexapterus Pacific sandlance Merluccius productus Pacific
    [Show full text]
  • J. Mar. Biol. Ass. UK (1958) 37, 7°5-752
    J. mar. biol. Ass. U.K. (1958) 37, 7°5-752 Printed in Great Britain OBSERVATIONS ON LUMINESCENCE IN PELAGIC ANIMALS By J. A. C. NICOL The Plymouth Laboratory (Plate I and Text-figs. 1-19) Luminescence is very common among marine animals, and many species possess highly developed photophores or light-emitting organs. It is probable, therefore, that luminescence plays an important part in the economy of their lives. A few determinations of the spectral composition and intensity of light emitted by marine animals are available (Coblentz & Hughes, 1926; Eymers & van Schouwenburg, 1937; Clarke & Backus, 1956; Kampa & Boden, 1957; Nicol, 1957b, c, 1958a, b). More data of this kind are desirable in order to estimate the visual efficiency of luminescence, distances at which luminescence can be perceived, the contribution it makes to general back• ground illumination, etc. With such information it should be possible to discuss. more profitably such biological problems as the role of luminescence in intraspecific signalling, sex recognition, swarming, and attraction or re• pulsion between species. As a contribution to this field I have measured the intensities of light emitted by some pelagic species of animals. Most of the work to be described in this paper was carried out during cruises of R. V. 'Sarsia' and RRS. 'Discovery II' (Marine Biological Association of the United Kingdom and National Institute of Oceanography, respectively). Collections were made at various stations in the East Atlantic between 30° N. and 48° N. The apparatus for measuring light intensities was calibrated ashore at the Plymouth Laboratory; measurements of animal light were made at sea.
    [Show full text]
  • Important Northeast Fish Provides Bait & Forage Needs
    Species Profile: Atlantic Herring Atlantic Herring Clupea harengus Important Northeast Fish Provides Bait & Forage Needs Introduction Atlantic herring (Clupea harengus) is a member of the clupeid family, which are typically small, schooling marine fishes, such as menhaden, shad, and sardines. This species is also known as sea herring because it spends its entire life cycle in the ASMFC Management Area: ME - NJ ocean (unlike the anadromous river herring). Atlantic herring inhabits the coastal Common Names: Sea herring, sar- waters of the United States from Cape Hatteras, North Carolina through Labra- dine, herring dor, Canada, and also off the coasts of Europe. Herring form the base of the food web as a forage fish for marine mammals, seabirds, and many fish throughout the Interesting Facts: * Atlantic sea herring are often Mid-Atlantic and Northeast. They are an effective and affordable bait source for confused with river herring. Sea lobster, blue crab, and tuna fishermen, and were historically sold by fish canneries herring spend their entire life at as sardines. Whale watching/ecotourism and salt retailers are indirectly dependent sea, while river herring migrate on a steady supply of herring because whales migrate inshore in pursuit of schooling annually to freshwater to spawn. * Atlantic and Pacific herring have herring and fishermen buy salt to preserve their fish. Overseas, frozen and salted been found to produce a burst herring are a valued commodity. of sound, called a Fast Repetitive Tick, at night. Its believed that The Commission’s Atlantic Herring Section manages herring in state waters (0 - 3 this high-pitched click-like sound miles from shore), while the New England Fishery Management Council (Council) is used by herring to signal their location, thereby making it easier regulates the stock in federal waters (3 - 200 miles from shore).
    [Show full text]
  • The Influence of Density in Population Dynamics with Strong and Weak Allee Effect
    Keya et al. J Egypt Math Soc (2021) 29:4 https://doi.org/10.1186/s42787-021-00114-x Journal of the Egyptian Mathematical Society ORIGINAL RESEARCH Open Access The infuence of density in population dynamics with strong and weak Allee efect Kamrun Nahar Keya1, Md. Kamrujjaman2* and Md. Shafqul Islam3 *Correspondence: [email protected] Abstract 2 Department In this paper, we consider a reaction–difusion model in population dynamics and of Mathematics, University of Dhaka, Dhaka 1000, study the impact of diferent types of Allee efects with logistic growth in the hetero- Bangladesh geneous closed region. For strong Allee efects, usually, species unconditionally die out Full list of author information and an extinction-survival situation occurs when the efect is weak according to the is available at the end of the article resource and sparse functions. In particular, we study the impact of the multiplicative Allee efect in classical difusion when the sparsity is either positive or negative. Nega- tive sparsity implies a weak Allee efect, and the population survives in some domain and diverges otherwise. Positive sparsity gives a strong Allee efect, and the popula- tion extinct without any condition. The infuence of Allee efects on the existence and persistence of positive steady states as well as global bifurcation diagrams is presented. The method of sub-super solutions is used for analyzing equations. The stability condi- tions and the region of positive solutions (multiple solutions may exist) are presented. When the difusion is absent, we consider the model with and without harvesting, which are initial value problems (IVPs) and study the local stability analysis and present bifurcation analysis.
    [Show full text]
  • Grade 3 Unit 2 Overview Open Ocean Habitats Introduction
    G3 U2 OVR GRADE 3 UNIT 2 OVERVIEW Open Ocean Habitats Introduction The open ocean has always played a vital role in the culture, subsistence, and economic well-being of Hawai‘i’s inhabitants. The Hawaiian Islands lie in the Pacifi c Ocean, a body of water covering more than one-third of the Earth’s surface. In the following four lessons, students learn about open ocean habitats, from the ocean’s lighter surface to the darker bottom fl oor thousands of feet below the surface. Although organisms are scarce in the deep sea, there is a large diversity of organisms in addition to bottom fi sh such as polycheate worms, crustaceans, and bivalve mollusks. They come to realize that few things in the open ocean have adapted to cope with the increased pressure from the weight of the water column at that depth, in complete darkness and frigid temperatures. Students fi nd out, through instruction, presentations, and website research, that the vast open ocean is divided into zones. The pelagic zone consists of the open ocean habitat that begins at the edge of the continental shelf and extends from the surface to the ocean bottom. This zone is further sub-divided into the photic (sunlight) and disphotic (twilight) zones where most ocean organisms live. Below these two sub-zones is the aphotic (darkness) zone. In this unit, students learn about each of the ocean zones, and identify and note animals living in each zone. They also research and keep records of the evolutionary physical features and functions that animals they study have acquired to survive in harsh open ocean habitats.
    [Show full text]
  • Swarm Intelligence
    Swarm Intelligence Leen-Kiat Soh Computer Science & Engineering University of Nebraska Lincoln, NE 68588-0115 [email protected] http://www.cse.unl.edu/agents Introduction • Swarm intelligence was originally used in the context of cellular robotic systems to describe the self-organization of simple mechanical agents through nearest-neighbor interaction • It was later extended to include “any attempt to design algorithms or distributed problem-solving devices inspired by the collective behavior of social insect colonies and other animal societies” • This includes the behaviors of certain ants, honeybees, wasps, cockroaches, beetles, caterpillars, and termites Introduction 2 • Many aspects of the collective activities of social insects, such as ants, are self-organizing • Complex group behavior emerges from the interactions of individuals who exhibit simple behaviors by themselves: finding food and building a nest • Self-organization come about from interactions based entirely on local information • Local decisions, global coherence • Emergent behaviors, self-organization Videos • https://www.youtube.com/watch?v=dDsmbwOrHJs • https://www.youtube.com/watch?v=QbUPfMXXQIY • https://www.youtube.com/watch?v=M028vafB0l8 Why Not Centralized Approach? • Requires that each agent interacts with every other agent • Do not possess (environmental) obstacle avoidance capabilities • Lead to irregular fragmentation and/or collapse • Unbounded (externally predetermined) forces are used for collision avoidance • Do not possess distributed tracking (or migration)
    [Show full text]
  • Report on the First Scotian Shelf Ichthyoplankton Program
    NOT TO BE CITED WITHOUT PRIOR REFERENCE TO THE AUTHOR (S) International Commission for a the Northwest Atlantic Fisheries Serial No. 5179 ICNAF Res. Doc. 78/VI/21 (D.c.1) ANNUAl MEETING - JUNE 1978 Report on the First Scotian Shelf Ichthyoplanktoll Program (SSIP) Workshop, 29 August to 3 September 1977, St. Andrews, N. B. Sponsored by Department of Fisheries and Environment Marine Fish Division Resource Branch, Maritimes Bedford Institute of Oceanography Dartmouth, Nova Scotia TABLE OF CONTENTS Page Abstract 2 Terms of Reference 2 Introduction 4 Oceanographic Regime •••••..••••.•.•.•••••••..••••••.••..•. 4 Overview of Present Approaches ••••••••••••••••••..•••.•••• 6 - Canada 6 - United States of America 13 - Un! ted Kingdom 19 - Federal Republic of Germany......................... 24 Sampling Recommendations 25 Sorting Protocols 26 Planning Sessions 26 Summary and Resolutions ••••••••.•..••...•••.••••...•.•.•.• 27 References 28 List of participants 30 Convener P. F. Lett Rapporteur: J. F. Schweigert C2 - 2 - ABSTRACT The Scotian Shelf ichthyoplankton workshop was organized to draw on expertise from other prevailing programs and to incorporate any new ideas on ichthyoplankton ecology and sampling 8S it might relate to the stock-recruitment problem and fisheries management. Experts from a number of leading fisheries laboratories presented overviews of their ichthyoplankton programs and approaches to fisheries management. The importance of understanding the eJirly life history of most fish species was emphasized and some pre! iminary reBul
    [Show full text]
  • Atlantic "Pelagic" Fish Underwater World
    QL DFO - Library / MPO - Bibliothèque 626 U5313 no.3 12064521 c.2 - 1 Atlantic "Pelagic" Fish Underwater World Fish that range the open sea are Pelagic species are generally very Atlantic known as " pelagic" species, to dif­ streamlined. They are blue or blue­ ferentiate them from "groundfish" gray over their backs and silvery­ "Pelagic" Fish which feed and dwell near the bot­ white underneath - a form of tom . Feeding mainly in surface or camouflage when in the open sea. middle depth waters, pelagic fish They are caught bath in inshore travel mostly in large schools, tu. n­ and offshore waters, principally with ing and manoeuvring in close forma­ mid-water trawls, purse seines, gill tion with split-second timing in their nets, traps and weirs. quest for plankton and other small species. Best known of the pelagic popula­ tions of Canada's Atlantic coast are herring, but others in order of economic importance include sal­ mon, mackerel , swordfish, bluefin tuna, eels, smelt, gaspereau and capelin. Sorne pelagic fish, notably salmon and gaspereau, migrate from freshwater to the sea and back again for spawning. Eels migrate in the opposite direction, spawning in sait water but entering freshwater to feed . Underwater World Herring comprise more than one­ Herring are processed and mar­ Atlantic Herring keted in various forms. About half of (Ctupea harengus) fifth of Atlantic Canada's annual fisheries catch. They are found all the catch is marketed fresh or as along the northwest Atlantic coast frozen whole dressed fish and fillets, from Cape Hatteras to Hudson one-quarter is cured , including Strait.
    [Show full text]
  • Why Study Bycatch? an Introduction to the Theme Section on Fisheries Bycatch
    Vol. 5: 91–102, 2008 ENDANGERED SPECIES RESEARCH Printed December 2008 doi: 10.3354/esr00175 Endang Species Res Published online December xx, 2008 Contribution to the Theme Section ‘Fisheries bycatch problems and solutions’ OPENPEN ACCESSCCESS Why study bycatch? An introduction to the Theme Section on fisheries bycatch Candan U. Soykan1,*, Jeffrey E. Moore2, Ramunas ¯ 5ydelis2, Larry B. Crowder2, Carl Safina3, Rebecca L. Lewison1 1Biology Department, San Diego State University, 5500 Campanile Dr., San Diego, California 92182-4614, USA 2Center for Marine Conservation, Nicholas School of the Environment, Duke University Marine Laboratory, 135 Duke Marine Lab Road, Beaufort,North Carolina 28516, USA 3Blue Ocean Institute, PO Box 250, East Norwich, New York 11732, USA ABSTRACT: Several high-profile examples of fisheries bycatch involving marine megafauna (e.g. dolphins in tuna purse-seines, albatrosses in pelagic longlines, sea turtles in shrimp trawls) have drawn attention to the unintentional capture of non-target species during fishing operations, and have resulted in a dramatic increase in bycatch research over the past 2 decades. Although a number of successful mitigation measures have been developed, the scope of the bycatch problem far exceeds our current capacity to deal with it. Specifically, we lack a comprehensive understanding of bycatch rates across species, fisheries, and ocean basins, and, with few exceptions, we lack data on demographic responses to bycatch or the in situ effectiveness of existing mitigation measures. As an introduction to this theme section of Endangered Species Research ‘Fisheries bycatch: problems and solutions’, we focus on 5 bycatch-related questions that require research attention, building on exam- ples from the current literature and the contributions to this Theme Section.
    [Show full text]