SolvingBycatch: Considerations for Todayand Tomorrow 219

ConservationAspects of FishingGear: Cetaceans and Gillnets

jon Lien Memorial University of Newfoundland, 230 Mount Scio Road, St, John' s, NF AZC 5S7 Canada

Gillnets are frequently identified as primary sourcesfor mortality in air-breathing marine animals including seabirds, turtles, whales, dolphins, and porpoise. In addition to conservation concerns for many local populations and species, the public attachment to these animals has placedurgent pressuresfor significant reductions in bycatch on fishing interests using gillnet technology. Failing reductions, area closures or total bans on gillnets are commonly sought by managers and the public, To defend themselves in the past, fishing interests have frequently denied or mini- mized bycatch extent or impact, and resisted past efforts to modify fishing practices or technologywhich reduce bycatch, Currently, such a strategy is less successfulbecause of the intensity of the public interest in ocean conservation and distrust of the industry. Without industry help, managers, scientists, and engineers have often not been successful in achieving practical bycatch reductions, With industry help, techniques have been developedto reducebycatch that appear promising. Such modifications of fishing technologyor operation must be basedon an understanding of the sensoryfunction and behavior of both target and bycatch species, as well as fishing practices, For instance, adding sounds to gillnets appears to be one approach that is effective in reducing bycatch of whales, dolphins, and porpoise, In the future, new partnerships between scientists, engineers, and fishing interests will be necessary to solve gillnet bycatch of these high profile species, A single whale, presented in the media while towing a gillnet which entraps it, is the worst possible advertising for gillnet fisheries, New technologyusing acousticalarms will be available to prevent gillnet bycatch of whales and dolphins, but practical implementation of effective reduction programs will demand new attitudes, cooperation, and joint efforts among all stakeholders.

whale caught in fishing gear can easily sector. The public's attachment to whales and dol- destroy nets or tow them away. This can phins has placed urgent pressures for significant A represent a substantial loss to fishermen, reductions in bycatch on fishing interests using Once a frightened animal is towing the gear, it gillnet technology. 13anson gillnet technology or can pose a serious threat to boats and other gear time/area closures are commonly suggested by in the area. Such an incident, reported to the pub- the public and managers as solutions. To defend lic, is like a huge billboard with an anti-gillnet themselves in the past, fishing interests have fre- message, One highly publicized whale caught in a quently denied or minimized bycatch extent or net, or even suspicions of undisclosed dolphin by- impact, and resisted efforts to modify fishing catch, can do much to destroy the image of a gear practices or technology that reduce bycatch. 220 J, Lein

Currently such a strategy is less successfulbe- provideexpert knowledgeof gear and fishing proce- causeof the intensity of the public interest in dures,and scientistsadd their expert knowledgeof oceanconservation and distrust of the industry. the animals and their environment.Alternative ap- For these reasons, fishermen must learn to deal proachesin which scientificor managementexperts constructively with this new hazard on the fish- imposetechnology or restrictions on fishery partici- ing grounds. pants generally meet with resistance from the in- It is likely that the problem will increase in dustry and in actual practicetake longerto be the foreseeablefuture. Due to whaling, the num- effectively implemented. bers of many whale specieswere seriously deplet- Without industry help, managers,scientists, ed. It is also known that indirect and incidental and engineershave had difficulties in achieving mortality of whales and dolphins due to fishing practical bycatch reductions. With industry help, operations has also seriously reducedsome popu- techniqueshave been developedto reducebycatch lations for example, see Perrin et al, 1994!. Such that appear promising. Such modifications of fish- reductions in a group of marine speciescan pro- ing technology or operations must be based on an duce serious impacts on oceanecosystems, and understanding of the sensoryfunction and behav- even on commercial fisheries Katona and White- ior of both target and bycatch species,as well as head 1988,Butman et al. 1994,Butterworth 1995!. fishing practices. Thus, managementactions in the United States, Canada,and in most nations have attempted to halt declinesin whale and dolphin populations WhyWhales and Dolphins Cet Caught in and to increase their numbers. This is a sensible FishingCear course, but while increased numbers of whales The exact factors which producecollisions and en- and dolphins may be goodnews indicating a tanglementin netsare little studiedand poorly healthyocean, it doespose a directchallenge to understood, Porpoise may fail to detect or attend fishermen who must cope with increased numbers to the nets, they may be attracted to fish in and of animals, and heightenedpublic awarenessof around the nets, or other factors. If incidental bycatch problems, catchesare the result of accidents,whatever the mixture of factors that actually lead to such en- A PartnershipBetween Fishermen counters, one approach to minimizing them would be to enhanceor amplify salienceof net cuesused and Scientists by the animal, thus making the net easier to de- For overa decadeand a half,scientific and engi- tect and define as a barrier Lien et al. 1995!. neering work to minimize bycatch of cetaceans in Much basic knowledgeof whales and dolphins, fishing gear has been conducted in the waters of and their behavior around fishing gear remains Newfoundland and Labrador I ien et al, 1995!. uncertain, Thus, the urgency prompting field Theseefforts have met with varying degreesof studies to reduce incidental catcheshas required successdepending on the animal, fishermen, gear efforts to be basedon commonsense and general type, and bycatch problem involved. approaches to accident reduction. The approach we have taken, which has been Accident prevention in most situations, what- detailed elsewhere Lien et al, 1992, 1995!, has ever the factors that actually produceaccidents, been to work cooperativelywith fishermen on a is basedon amplification of existing cuesin the problem for which they are responsible.We have object or barrier, or enhancementof the object's resisted the urge to define bycatch as a scientific detectibility by adding additional cuesto its loca- or managementproblem, becomethe goodguys, tion or characteristics, Thus, for humans, fire hy- and solve it for them, Our approachis slow and drants are brightly painted, sirens are used on presents difficulties for the scientist; but in the emergencyvehicles, edges of steps are painted in end, both scientist and fishermen have gained high contrast strips, etc. Such an approachwith from such partnerships and in generally they animals includes use of whistles on vehicles to have been effective in achieving reductions of ce- minimize road kills, patterns placed on windows tacean bycatches.Such an approachto bycatch to prevent bird strikes, etc. The actual success of solutions is not unique; there are other more no- such approachesvaries dependingon the nature table examples,such as the cooperationwhich of the environmental threat, conditions that pro- has slowly reduced dolphin bycatches in the tuna duce the accidents,and a variety of specieschar- industry. Within these partnerships fishermen acteristics Lien et al, 1995!. SolvingOycatch: Considerations for Todayand Tomorrow 221

Whales are believed to primarily orient to al. 1991!. These alarms are large, were made for objects such as fishing gear using either passive permanently fixed gear, and are not appropriate or active acoustics Todd 1991!. Thus, acoustical for lighter gillnets. However, at the request of cues added to fishing gear might indicate to the fishermen, they were used in a pilot effort to as- whale that something is ahead and facilitate sess whether or not sounds added to gillnets detection and/or detour behaviors, For smaller would have any effect on bycatches. The alarms cetaceans, early encounters with nets lead to were adapted for placement on the headrope of entanglement and death; in such cases, no groundfish gillnets; experimental strings had learning about avoiding nets occurs. Enhanced alarms on each end, and eight additional alarms acoustical properties of nets may facilitate ini- evenly spaced along the string. Sounds from tial net detection by young or inexperienced an- alarms could be heard at both ends of even the imals. Repeated exposure to, and use of, these longest strings from. the middle of those strings cues could facilitate learning to effect net avoid- with hydrophones,I< ach fishing crew used two ance and detour behaviors Jefferson et al. strings with alarms total of 2,468 net days!; oth- 1992!. A focus of the research in this area has er strings used by these fishermen served as con- been to select sounds that are effective in get- trols total of 5,562 net days!. Observers recorded ting the animal's attention, planning ways of numbers of marine mammals caught in the nets. placing acoustic devices on gear to define the They also recorded numbers of seal-damaged fish, net as a barrier, and making such net add-ons and ensured that each alarm was functioning. compatible with fishing operations, During the experiment, 10 harbor porpoise were caught, all in control nets. While the fisher- men all agreed that the large codtrap alarms ACOUSTIC ALARM FIELD TESTS were not compatible with normal fishing of gill- HumpbackWhales and Codtrap Collisions nets, they felt strongly that the alarms were ef- fective in preventing porpoisebycatch Lien et al. Large humpback whales frequently collide with 1995!. and become entrapped in fishing gear in New- foundland Lien 1994!, Most costly to fishermen are those cases in which the whales collide with An AcousticAlarm Designed for Harbor codtraps. Acoustic alarms that produced sounds Porpoiseand Gillnets to which the whales were attentive, and which codfish could not hear kHz at 135 db re 1 An alarm specifical'Iy designed for groundfish gill- micropascal at 1 m at 3 s intervals! were devel- nets and harbor porpoise was available in 1993 oped Lien et al. 1992! and placed on fishing and was tested in a similar experiment in New berths that had histories of whale problems. England. These alarms are much smaller and These berths averaged 1.4 whale collisions/year vary individually in the sound that they produce; in previous years. Other high risk berths where harmonic patterns vary, as does the amplitude. traps had no alarms were also monitored. A to- The base frequency is a 2,5 kHz 1 s pulse, repeat- tal of 4,150 trap days were monitored. Probabil- ed every 2 s, The PVC pipe housing for the elec- ity of a collision per fishing day was signifi- tronics emphasizes harmonics of the basic sound cantly different; traps without alarms were so there is a broad frequency pattern of energy up three times more likely to have a whale colli- to 17.5 kHz. Amplitude is about 115 db re 1 mi- sion, and gear losses due to whales were also cropascal at 1 m. The base frequency is at 2,5 three times as high. Best of all, fish catches by kHz. traps with acoustic alarms were on average sig- The experiment, was organized in a manner nificantly higher not becauseof any effect on similar to the 1992 study except that only one end the fish. Codtraps without whale holes in them of a string and the ! irst five nets were fitted with simply fish better Lien et al, 1992!. alarms; the rest of the string had no alarms on it. Additional strings without any alarms were also used as controls. Attemptsto ReducePorpoise Bycatch During nearly 11,000net days which were ob- in Gillnets served 0% nets in no alarm strings; 25% no The codtrap alarms were used in 1992 to add alarm nets in experimental strings, and 15% sounds to groundfish gillnets that fished in New alarmed nets! a total of 39 marine mammals were England where porpoise bycatch is high Smith et caught 3 harbor porpoise, 4 dolphins, and 2 222 J. Leis seals!.All but one animal was caught in no alarm it is the density and pa.ttern of attachment that nets indicating that porpoise are 4.6 times more is important. likely to become entangled in non-alarmed nets that in nets with added sound. Further tests of the gillnet alarm for harbor DISCUSSION porpoisehave been conductedin the Bay of Lower numbers of whales and dolphins have con- Fundy, Canada,an area reported to be high in sistently been caught in traps and nets fitted harbor porpoisebycatch Gaskin 1991,Tripple with acoustical alarms. However, there were 1994!. In this area, each fisherman typically uses many constraints inherent in planning and con- 4-5 strings of three webs.Alarm strings were fit- ducting the investigations. ted with four of the gillnet alarms one on each Given the low probability of actually catching end, and at eachbridle!, Control strings were of a porpoise on any net day, and the likelihood that two types. One set of control strings was fished any net modification wi]1 work at less than 100% without alarms, the secondset of control strings efficiency,the experiments were handicapped was fished with alarms that did not emit, sounds. from the outset, and basically lacked the statisti- Non-functioning alarm strings were used to ex- cal power to demonstrate alarm effectiveness amine whether or not the alarm changedfishing clearly. Each experiment,would, conservatively, effectivenessin any way.A string was randomly have to be doubled for adequatestatistical power, designatedas an alarm or control string at the It is clear that acoustic alarms can reduce inci- time it was first placed in the water, and alarms dental entrapments of harbor porpoisein gillnets. were placed on the string at that time. Each fish- The degreeto which bycatch can be minimized by ing day was monitored by an observer and catch- add-on sounds,the cost ffectivenessof this ap- es of target and nontarget fish speciesand proach for fishermen, management costs/benefits bycatch was recorded. of this approach compared to alternative conser- There were no differences in number of fish vation measures such as effort control, time/ taken between experimental conditions. A total of area closures, and quotas all remain to be com- 43 harbor porpoisewere caught during the sum- pletely determined. mer. Mean catch per net day was 0,016; 0.010 in However,as a whole, the experiinents using acoustic alarm nets, 0,018 in silent alarm nets, acoustical alarms on groundfish gillnets to reduce and 0,019 in control nets. The difference between harbor porpoisebycatch are extremely promising. acousticalarmed nets and control nets is signifi- Without exception,fishermen participating in cant but not as dramatic as in earlier tests. each experiment have become convinced that the Acoustic alarms were sometimes recorded at dis- alarms reducebycatch. Each of the present stud- tances up to 50 m from source, although the ies showed much lower bycatch rates in alarm- alarm signal was difficult to detect at that dis- protected nets. Fishermen clearly have the tance. At times, however, it was difficult to hear opportunity to work further with scientists to re- alarm noise at distancesgreater than 25 m, Thus, ducebycatch of whales and dolphins using acous- the signal to noise ratio observedin this experi- tic alarms. ment is believed to have effected results and During the course of'these experiments, made alarms less effective. coinmunication channels that developedbe- To check this, in 1995 the experiment was tween fishermen and scientists greatly im- repeated using the same alarms but using 10 proved. Fishermen gained greater familiarity equally spaced alarms on a string of 3 nets for with marine mammals and strategies to modify the experimental condition; strings with no fishing gear to reduce bycatch, and took respon- alarms were used as controls, Under this cir- sibility for solving the bycatch problem them- cumstance, the net as a barrier was well-de- selves. Marine mammalogists gained experi- fined even in spite of high ambient noise and ence with the technology and the ways of relatively quiet alarms. To date, 24 92%! por- fishermen. Gear techno.logistslearned the ways poise have been taken in no alarm nets which of marine maminalogists. Fishermen gained account for 60% of the observed fishing effort; 2 sufficient experience with alarm effectiveness animals 8%! have been taken in alarm nets to encourage further cooperative work with sci- which account for 40% of the observed fishing entists on acoustic alarms to reduce whale, effort. This would seem to indicate that alarms dolphin, and porpoise bycatch. That, work must need not be excessively loud to be effective, but continue. SolvingBycatch: Considerations for Todayand Tomorrow 223

ACKNOWLEDGMENTS Katona, S. and H. Whitehead. 1988. Are cetacea ecologicallyimportant? In: M. Barnes [ed.], Funds for the development of alarms in 1992 Oceanography and marine biology: Annual re- were provided by the Centre for Fisheries Innova- view, Aberdeen University Press, pp. 553-568. tion CFI! in grants to Jon Lien and Jacques Guigne, The Department of Fisheries and Oceans Lien, J., C, Hood, D. Pittinan, P. Ruel, D, Borg- DFO! provided funds to Jon Lien for these tests. gaard, C. Chisholm, L. Wiesner, T. Mahon, New Hampshire Sea Grant also provided some and D. Mitchell. 1995. Field tests of acoustic funds to assist in testing. The National Marine devices on groundfish gillnets: Assessment of Fisheries Service NMFS! further assisted in the effectiveness in reducing harbour porpoise by- tests by authorizing additional fishery observer catch. In R.A. Kastelein, J.A. Thomas, and effort in the project. Funds for gillnet alarm de- P.E. Nachtigal [eds.] Sensory systems of velopment were supplied by DFO. NMFS provid- aquatic mammals, De Spil Publisher, Woer- ed some funds for constructing the required den, The Nethe> lands, pp. 349-364, number of alarms for the 1993 experiment and supplied two Sea Sampling Observers.Funds for Lien, J. 1994. Entrapments of large cetaceans in the three Memorial University of Newfoundland passive inshore fishing gear in Newfoundland observers were supplied by academic grants to and Labrador 979-1990!. Report of the Inter- Jon Lien. Funds for experiments in the Bay of national Whaling Commission, Special Issue Fundy in 1994 were provided by DFO and the 15: 149-157. New Brunswick Department of Fisheries and Aquaculture. Lien, J, and C. Hood. 1994. An investigation of We especially acknowledge the assistance and acoustic devices to prevent harbour porpoise by- cooperationprovided by the fishermen with whom catch in groundfish gillnets, and recommenda- we worked in these studies. They helped in rig- tions from fishermen in the Bay of Fundy for ging alarms to fit gillnets and endured our con- future bycatch mitigation. Department of Fish- stant observation and our endless questions. It eries and Aquaculture, Government of New was a pleasure to work for them, Special thanks Brunswick, Fredricton, NB, 21 Nov., 23 pp. is also due the observers who participated in the studies. Without their fine efforts, our work Lien, J., W. Barney, S. Todd, and R, Seton. 1992. would not have been possible. Effects of adding sounds to cod traps on the probability of collisions by humpback whales, In: J.A. Thomas, R.A. Kastelein and A,Y. Su- REFERENCES pin [eds.], Marine mammal sensory systems, Butman, C.A,, J,T, Carlton, and S.R. Palumbi. Plenum Press, New York, pp. 701-709. 1995, Whaling effects on deep-sea biodiversi- ty. Conservation Biology 9!;462-464. Lien, J., S. Todd, and J. Guigne. 1990, Inferences about perception in large cetaceans, especial- Butterworth, D.S. 1995. On modelling approaches ly humpback whales, froin incidental catches for evaluating sea-fishery interactions: Initia- in fixed fishing gear, enhancement of nets by tives in South Africa and for the Antarctic. "alarm" devices, and the acoustics of fishing NAFO/ICES Symposium on the Role of Ma- gear. l'n: J,A, Thomas and R.A. Kastelein rine Mammals in the Ecosystem. 3,1, North- [eds,], Sensory abilities of cetaceans, Plenum west Atlantic Fisheries Organization, Press, New York, pp. 347-362, Dartmouth, NS. Perrin, W.F., G,P. Donovan, and J. Barlow. 1994. Gaskin, D.E. 1991. Status of the harbour por- Gillnets and cetaceans, Report of the Inter- poise, Phocoena phocoena, in Canada. Canadi- national Whaling Commission, Cambridge, an Field-Naturalist 106!:36-54. Special Issue 15, 629 pp.

Jefferson, T.A., B. Wursig, and D. Gertl, 1992. Ce- Smith, T.D., D. Palka, K. Bisack, and G. DiNardo. tacean detection and responses to fishing 1991. Preliminary estimates of harbor por- gear. In: J.A. Thomas, R. Kastelein and AY, poise abundance and bycatch. NRFSC Refer- Supin [eds,], Marine mammal sensory sys- ence Document 91-04, Northeast Fisheries tems, Plenum Press, New York, pp. 663-684, Science Center, Woods Hole, MA. 224 J. Lein

Todd,S.K, 1991.Acoustical properties of fishing gear: Possible relationships to baleen whale entrapment. M.Sc. Thesis, Queen Elizabeth II Library, Memorial University of Newfound- land, St, John' s, NF, 213 pp,

Tripple, E. 1995.Harbour porpoisebycatch in the Bay of Fundy gillnet fishery: Project Summa- ry. Industry Servicesand Native Fisheries, Fisheries and Oceans,Scotia Fundy Region, Halifax, NS, 4 pp. SolvingBycatch: Considerations for Todayand Tomorrow 225

Public Awarenessof Bycatch issues and Political Pressurefor Change

Donald D. Stuart Salmon for Washington,4209 21st Ave. W, ¹301, Seattle, WA 98199

In state after state in recent years, we in commercialfisheries have faced a flood of legislative issues and initiative battles. Many of these have addressedbycatch. The public generally doesn't understand bycatch issues,but they do understand that there is a problem and they are demanding that it be solved.The latest of these public bycatch battles is Initiative 640 in Washington. While very poorly drafted, I-640 demonstrateshow public concernabout bycatch can easily translate into broadsideattacks on the commercial industry by our worst enemies,and it proves how vulnerable we can be if we do not stay 100% on top of this issue.

ycatch in fisheries is a ticking bomb; a That is why bycatch is much more than just bomb that has been set off many times in a public relations problem. It is real, We must recent years in state legislatures around deal with it realistically, or that ticking bomb the country, in Congress, in public ad campaigns, will go off in our faces, and in initiatives and referendums to the voters. The reality and explosiveness of bycatch is- Very often, it seems, when this bomb has been sues has come home to those of us in Washington detonated, it has not been by friends, and often not recently with the certification for the November for the highest of motives. Rather, usually, it is by 1995 election ballot, of Initiative 640, our home- people who have some economic or political ax to grown version of the net-ban mania that is grind; by people whose motivations are suspect. sweeping the country. With I-640, the growing However, the eA'ectshave been the same: damage to public awareness o!'bycatch issues placed a fisheries with very little benefit to the fish, weapon in the hands of bitter enemies of com- We in fisheries must deal with bycatch issues mercial fisheries. With bycatch, Washington's within our industry, or ill-intentioned people will good ol' boy network of avid recreational fishers deal with it for us. saw their opportunity to eliminate their only re- It is sometimes difficult for those of us who maining competition for the salmon resource- fish for a living to see that what we do is a public and they went for it, as they have done lately in matter, We feel that once we untie from the dock, other states, like California, Florida, North Caro- round that point, and disappear over that hori- lina, Louisiana, and Oregon. In nearly every in- zon, no one really knows or cares what we do on stance, the themes of these campaigns of our own boat in our own way. But that is not the distortion and self-interest have been the same: case. In fact, the reverse is true, Most of what "Eliminate wasteful fishing practices!" "Get out happens in our industry is intensely public. What the nets!" "Save sea life!" happenshere in Washington affects peoplein Recently, I was in a debate on the initiative New York, California, or Alaska. What happens in right here in Seattle. A former TV newscaster Florirla, affects us in Washington. And in an open was one of the speakers. I think it's fair to say democratic society, that's the way is should be, that this gentleman is not a noted expert on and it's the way it always will be. bycatch issues. Nonetheless, he was sufficiently 226 D,D, Stuart knowledgeable to repeat the hot buttons and ticipated voluntarily, knowing that if they were to catch words over and over again: "Wasteful fish- solve the problem, that was their best course. ing." "Walls of death." "Thousands of seabirds Ask yourselves what use has been made so far killed daily." "Untold numbers of marine mam- of the information producedin this cooperativepro- mals slaughtered.""Deadly ghost nets," cess?It will probablybe reflectedin next year's fish- A member of the audience was astute ery regulations for Puget Sound if there is such a enough to ask him just what he meant by fishery.The principle use has beento providestatis- "Wasteful fishing." In response to this question, tical bycatchammunition to the pro I-640 campaign another of the I-640 proponents stood up with a in their public effort to vilify the commercial indus- picture from the front cover of a recent issue of try and to eliminate the Washington fleet. Fisheries magazine showing nontargeted Wheneverwe all sat down at meetings on bycatch in a shrimp trawl fishery in the gulf off this, hopefully, cooperative process in our effort to Florida. What happens in Florida, affects us find answers to bycatch, who do you supposewas here; when the bycatch bomb goes off in Flori- present? A representative of the pro I-640 folks da, we feel the impact. duly taking notes. Never did this individual have Three years ago, the EndangeredSpecies Act any helpful answersto provide. No, he was gath- ESA! listing of the marbled murrelet caused the ering ammunition. We all knew that the next U,S. Fish and Wildlife Service USFWS! to be- time we saw the material discussed or handed out come concerned with the catch of seabirds in the during that meeting, it would be in the press, Puget Soundnet fisheries. Our local fieet recog- When asked about his reasonsfor being present nized the need to deal pro-actively with this is- at one of these meetings, the I-640 representative sue, and we entered into a cooperativeprocess simply said, "It's a public meeting. I have a right with USFWS, with the Tribes, and with Audubon, to be here." That was true; it was, and he did, to find solutions, That's how an open democratic system works. To date, this processhas produced: I! an ini- In politics it is sometimeshard to weigh the tial review to determine if there was a problem relativeimportance of appearanceand reality. I with murrelets; there was not, but there were say it's 50-50, exactly 50-50, That's because the concernsabout other bird species!,! a compre- minute you start to think reality is more impor- hensive study of the extent and nature of bird im- tant than appearance,something like I-640 comes pacts in net fisheries in Puget Sound a must if along to prove you wrong. The minute something we are to deal with this problem!, and 8! a study like I-640 starts you thinking that appearanceis of potential gear and fishery modifications de- more important than reality, something like this signed to identify solutions, bird issue proves you'r e wrong as well. Much of the expense, coordination, labor, and Those of us in fisheries have learned to face risk for doing this work camestraight out of the the need to deal with both appearanceand reali- fishing industry not at the expenseof the public. ty. If we do not do so, sooneror later that bycatch Much of the credit for accomplishingso much in bomb will blow up in our facesjust like it has so so short a time is owedto the fishermen who par- many times before, Solving Bycatch: Considerations for Today and Tomorrow 227

Size Selection in Purse Seines

Arvid K. Beltestad and Ole Arve Misund Insti tute of Marine Research, P.O. Box 1870, N-5024 Bergen, Norujay

In purse seinefisheries, size selectionmay be required becausesome of the fish in the catch are less than the legal size and/or because different size groups have different market prices. In Norway both are relevant in the coastal purse seinefishery for saithe Pollachius Uirens!,and even moresoin the North Sea mackerel Scomberscombrus! fishery. The Institute of Marine Research has developed a new technology for size selection of fish in purse seinesbased on the use of rigid metal sorting grids, The grid is mounted on the bunt of the seine when the net is being hauled back and thereafter lowered into the sea by use of the main deck crane. %hen the catch is concentratedin the bunt alongside the vessel, small fish below a certain size escape between the grid bars, The sorting efficiency achievedhas been good and the measured size selectionrange very narrow. Preliminary trials indicate about 60% survival of escapedmackerel and no mortality of saithe.

ycatches of marine mammals, birds, and of the purse seine alive, thereby increasing the unwanted fish species are not common in proportion of mackerel above 600 g in the catches, Norwegian purse seining, The only excep- this would increase the value of the catches and, tion may be a relatively small fraction of cod thus, the income of the fishermen. A 10% increase caught during purse seining for capelin and her- in the proportion of mackerel above 600 g would ring. raise income by approximately US$80,000per Unlike trawling, longlining, and gillnetting, vesselper year, If most of the mackerel that es- purse seining has traditionally been categorized cape through the sorting device survive, this will as a non-selective fishing method, aimed to catch also lead to better stock management. all sizes of fish. Most countries in the world there- In the purse seine fishery for saithe, fishing fore have no mesh size regulation for purse sein- grounds very often have to be closedbecause of ing in their fishing regulations. the large proportion of undersized fish in catches. In Norway, the demand for size-selective Closing fishing grounds reduces income since purse seines has been increasing in recent years, fishing vesselshave to leave those grounds and especially in the mackerel and saithe fisheries. search for new grounds with larger fish. Most of the mackerel caught by Norwegian purse There is a similar price differentiation with seiners are frozen and exported to Japan. The regard to fish size in the saithe fishery to that in Japanese market favors large mackerel above the mackerel fishery. 600 g and it pays twice as much for large fish, Metal sorting grids have been developed and Mackerel schools in the North Sea consist of dif- successfully introduced in shrimp and bottomfish ferent year classes and, therefore, different size trawls Isaksen et al. 1992, Larsen and Isaksen groups. It has been claimed that fishermen sort 1992!, Danish seine, and in salmon farining, In the fish onboard and discard the smallest macker- 1992, the Fish Capture Division of the Institute of el. If such a discarding process is of any magni- Marine Research started to develop a new tech- tude, this is bad exploitation of the mackerel nology for size selection of saithe and mackerel in stock. If the smallest mackerel could be sorted out purse seines based on rigid metal sorting grids 228 A.K. Beltestad 8 O.A. Misutid

mounted on the breast of the purse seine Misund the inter-bar distance was adjusted to 44 mm and and Beltestad 1994!, The first trials were con- then to 42 mm. The weight of the grid was about ducted on saithe in net pens Misund and Skeide 220 kg, 1992!. This year a new grid was built and tested. However,a fundamental issue regarding use The frame of this grid was made of 75 mm alumi- of sorting grids for size selectionin purse seines num tubing and with bars of 20 mm Glassfibre is whether fish survive after escape.Most of our Reinforced Polyester GRP!, The distance be- research during the last two years has therefore tween the bars was 42 mm. The size of the grid been aimed at measuring the survival rates of the was 3x3 m, and it weighed about 160 kg, escaped fish. The grid was mounted on the bunt of the purse seine by the follow ing procedure: when the MACKERELEXPERIMENTS pursing of the seine was complete, the breast of the seine was hoisted on deck by the main deck In order to determine whether nets could be used crane and securedto the rail by a rope.The for size selectionin mackerel purse seines,two breast line of the bunt was then laced to the grid panels of relatively large-meshed,stiff, impreg- by an 8 mm twisted line. After most of the seine nated net were mounted in the bunt of a tradi- had been hauled back, the grid was attached to tional mackerel purse seine, One panel was made the crane, and the net released from the rail and up of 4 mm braided knotted netting with a mesh hoisted overboardtogeth.er with the bunt. The size of 84 mm stretched meshes!. The other con- grid was lowered into the sea until most of it was sisted of 9 mm knotless ultra crossnet produced submerged.When the purseseine was drying up by Nichimo, Japan, with a mesh size of 90 mm. the catch alongsidethe vessel,the grid formed a Both net panels were mounted in a section of the "wall" in the bunt Fig. 2!. During the drying-up bunt directly under the selvageand about 25 m process,the fish were forced toward the grid. Af- from the breast of the purse seine.The panels ter the selection processwas completeand the were 9.5 m long and 3.5 m deep. catch had been pumped onboard,the grid was The first metal sorting grid tested was de- hoisted up alongsidethe rail and the purse seine signed for use in conventional mackerel purse released, seines used in the North Sea. The grid consisted All trials were carried out with conventional of an aluminum frame with bars of stainless steel North Seapurse seines for mackereland herring. of 25 mm diameter Fig, 1!, The size of the grid The first experiments on size selection of was 3x3.5 m, which gave a selection area of about mackerel in purse seining were performed on a 10m'. The distancebetween the barswas origi- cruise made by the chartered purse seiner M/V nally 40 mm. In the courseof the experiments, Selvaag Senior 7,5 m Loa.! in the North Sea in November 1992.The net panels were tested on the first five catchesand the mackerel grid on three succeeding catches. The inter-bar distance in the first two trials wa: 40 mm, and before the last trial the bar distance was adjusted to 44 mm. lggxiggx4 4 aml i ~ium In order to collect fish that had escaped through the grid, a shrirrip trawl bag was mount- lggx15 olumrnium ed on the mid-section of the seine on the outer side of the grid. The collection bag was about 10 m long and coveredabout one-ninth of the grid Bor distance45 Pped25 x 1,2 area, In order to provide length and weight mea- Stemlesssteel surements, samples of 100-200 individuals were taken from the collection bag and from the catch that waspumped onboard after the selectiongrid had been in action for about 15 min. orl.ing grid for mackensl nt seigntappr ox 222 The experiments cont,inuedin September cele1r25 1993 and 1994 along the western coast of Norway ll meosuree i ~mm by the chartered purse seiner M/V Ligrunn 7 m Loa,! The grid was the same as that used in the Figure 1. Prototypesorting grid for mackerelpurse 1992 trials, but the inter-bar distance was modi- sei ne. fied to 42 mm. Solving 8ycatch: Considerations for Today and Tomorrow 229

Figure 2. Sorting grid mounted in a mackerel purse seine.

hole In 1995 experiments were carried out with the chartered purse seiner M/V Grete Kresti n ed profilewelded 4.6 m Loa.!. During this cruise the new grid frorhetube with its aluminum tubing frame and GRP bars Ided was tested. The bar distance was 42 mm during these trials. Investigation of the survival rate of mackerel escaping through the grid started in 1998 by M/V Ligrunn and was carried out using the following procedure: for each trial, one control and one ex- perimental group were establishedby collecting and storing the fish in 25x10x10 m net pens, The control group was established by lacing the float- line of the net pen to the floatline of the bunt and submerging it by means of weights. The mackerel swam freely to the net pen as the purse seine was carefully dried up. The experimental net pen was laced to the outer side of the grid and collected all the fish that escaped through the grid. The two net pens were then towed slowly at about 0.5 m/s! inshore and moored. Survival rates were checked weekly for up to one month.

SAITHE EXPERIMENTS Experiments on size selection of saithe in purse scincs werc carried ont according to almost iden- tical methods as for mackerel. Since the mini- Figure 3. Present version of the sorting grid for saithe mum legal size of saithe varies along the purse seine. 230 A.K. Beltestad 8 O.A. Misund

Norwegian coast, from 30 cm in the south to 40 few fish becamegilled betweenthe bars, mostly cm in the north, inter-bar distances from 30 mm above the horizontal reinforcements. Selection to 40 mm were tested. continued for as long as the mackerel were active- The first size selection experiments were car- ly swimming in the bunt, which was up to about ried out with R/V Fj ordfangst 4.7 m Loa,! in one hour for catches of up to about 400 tons. The April 1994 in western Norway. The grids were de- selectionprocess gradually declined as the fish signed for a small experimental purse seine of becameexhausted and thereafter died, probably 320 m length and 45 m depth Misund et al. due to oxygen depletion. The dying and dead fish 1992!. One of the grids tested was made of alumi- sank to the bottom of the bunt. num and had dimensions of 2x2 m with an inter- The selection curves for the 40 mm and 44 bar distance of 35 mm. The other grid was of GRP mm inter-bar distancesof the mackerel grid were and measured 1x2 m with an inter-bar distance of quite sharp, with regard both to the length and 30 mm. the weight of the mackerel Fig. 4!. However, the In order to collect samplesfor length mea- selection curves do not approachzero retention surements, a small net pen x3x3 m! was laced for the smallest fish sizes. This is because some of to the outer side of the grid. Sainples of about 100 the small fish in the catch did not come into con- individuals were taken from fish passing through tact with the grid and therefore were unable to the grid into the collecting pen and from the catch escape. It should be noted that the increase in in- that remained in the purse seine. ter-bar distance from 40 mm to 44 mm increased Two net pens with saithe sorted through the the 50% retention length. by about one cm from grid were stored for one month in order to deter- 36 cm to 37 cm!, and the 50% retention weight by mine the survival rate of the escaped fish. about 80 g from about 420 g to about 500 g!. Sub- In August 1995 new selection trials for saithe stantial amounts of small mackerel were sorted were carried out with the chartered purse seiner out during the tests with the 42 inm bar distance, M/V Nargtind 2.77 m Loa,! off the coast of but the selection curves for these trials are not Finnmark in northern Norway. The main aim of presented here because inaccuracies in the inter- these trials was to measure the survival rate of bar spacing seems to have seriously influenced the saithe that escaped, the selection properties, The grid used during these trials Fig. 3! was During three sets of trials in 1995 all the made of aluminum tubing and 15.5 mm GRP bars mackerel that were sorted out through the grid with an inter-bar distance of 40 mm. It measured were collected in a net pen mounted on the outer 2x2 m and weighed about 60 kg, side of the grid. The sorting rate varied from 25% Three sets of survival trials were conducted to 40% of the total catch, and the proportion of by similar procedure as for mackerel. The net mackerel above 600 g increased by about 10% af- pens were moored close to the shore and the fish ter one hour of selection i',Table 1!. were stored for one week. The survival trials were conductedby M/V Ligrunn about 10 nautical miles off the west RESULTS coast of Norway, One control group and one ex- perimental group were established for each trial During the five selection trials with net panels in and the net pens were towed inshore and moored. the mackerelpurse seineof M/V SelvaagSenior in The whole operation took approximately 24 1992, most of the meshes both in the knotted and hours. The fish were stored in the net pens for the knotlessultra crossnet soonbecame clogged by about one month. The first trials resulted in a gilled mackerel.Size selection through thesenet 35% survival rate among the mackerel which had panelstherefore stopped rather quickly.The gilled escaped through the grid and a 55% survival rate fish alsoreduced the friction in the net hauling sys- for the control group which swam directly from tem and madehauling the net more difficult, espe- the purse seine into the net pen. The second trial cially for large catches, up to 220 tons. gave a survival rate of 56% and 95% respectively. In the trials using the mackerel grid, the se- The size selectionof: aithe in purse seine car- lection processstarted when the schools"explod- ried out in western Norway in 1994 gave a very ed" during drying up the catch in the bunt of the sharp selection curve with a 25%-75% selection purse seine. Substantial amounts of small fish range of only about 3 cm Fig. 5!. The 1995 exper- were observed escaping through the grid. Fish iments showed that up to 50% of the total catch of that were too large to pass through, rapidly swam saithe was sorted out through the grid within 15 away from the grid and back into the bunt. Just a Ill in. SolvingByeatch: Considerations for Todayand Tomorrow 231

100 Inter-bar epaatng Inter-b r paatng 90

80

70 V, 60 U 50

U 40 0 30

20

10

25 30 35 40 45 Length cm!

100 ~ 0 0 0 0 0 0 Inter-ba Inter-ba 90

80

Y, 60

50 c

U 40 I 30

20

'10

100 200 300 400 500 600 700 800 Weight g!

I'igure 4. Length topj and weight bottom>selection curves for mackerelwith 40 and 44 rnrninter-bar spacing in the sorting grid. 232 A.K. Beltestad 4 O.A. kfisund

Table 1. Sorting capacity.

Total Sorted Sorting Fish > 600 g Fish > 600 g catch by grid capacity total catch retained catch kg! kg! %! %! %! BO 77000 19000 25 38 42 41000 16000 39 24 31 70 65000 24000 37 43 53 60

50

tc 40 The experiments on survival of saithe that es- caped through the grid, carried out both in west- ern and northern Norway, resulted in no mortality in either the control or the experimen- 20 tal groups.

10 DiSCUSSION The selection experiments using rigid metal grids in mackerel and saithe purse seines showed that such devices can be used for size selection of fish Length lcm! in purse seines. Large amounts of fish were sort- ed out through the grids used in the mackerel Figure 5. Length selection curve with saithe for a and saithe purse seines,The sorting capacity will 30 rnm inter-bar spacing in the GPR sorting depend on the inter-bar distance and fish size. grid for saithe. Experiments using net panels for size selec- tion in mackerel purse seines showed that mesh clogging by gilled fish prevented effective selec- 1995 trials showed that it is possible to use bars of tion through such panels in purse seine bunts. GRPto reduceweight. Another advantageof these Gilled fish in meshes in the bunt also created dif- bars is that they have a certain degreeof flexibility, ficulties during hauling caused by reduced fric- so that they return to their original shape if slightly tion in the net hauling system. bent during handling. Stainless steel bars were eas- Mounting and handling of the rigid grids was ily bent during handling, and the selectionproper- accomplishedwithout great difficulty for both ties of the grids changed accordingly. mackerel and saithe purse seines, However, the The selection curves of the rigid grids were fair- first mackerel grid was large and heavy, necessi- ly sharp, and selection occurred within a narrow tating handling by hydraulic crane. The grid range of sizes. For the mackerel grid, which was occupiedsubstantial deck space,and mounting tested on large catches up to about 400 tons, the left and handling the grid may be a dangerousopera- part of the curve did not approach zero retention. tion for the crew if not conducted carefully. How- This is because large amounts of small mackerel did ever, the latest version of the grid was much not reach the grid and becomesorted out, but were easier to handle than the first one, The saithe instead pumped onboard, [n order to obtain high grids were so small and light that they could be catch quality, pumping had to start almost immedi- handled manually. Obviously,it is possibleto fur- ately after the catch was concentrated in the bunt ther develop the design, construction, and hand- and the selectionthrough the grid started. Even ling of rigid size selection grids for purse seines, though somemackerel started to die quite rapidly In small purse seines,it is possibleto use light in the bunt, the high sorting rate of up to 40% of the construction of synthetic materials. For larger total catch showed that a lot of mackerel were able purse seines,rigid grids must be strong enoughto to escapethrough the grid even after one hour of withstand substantial forces when handling concentration in the bunt. catches of several hundred tons. Such grids The selection experiments with saithe were should probably be built with a metal frame. The conducted with much smaller quantities of fish, SolvingBycatch: Considerations tor Todayand Tomorrow 233 and all the fish in the catches eventually came REFERENCES into contact with the grid. The left part of the selection curve for the 30 mm saithe grid there- Isaksen, B., J.W. Valdemarsen, R.B. Larsen, and fore approached zero retention. It is possible L. Karlsen, 1992, Reduction of fish bycatch in that all the fish may eventually come in contact shrimp trawl using a rigid separator grid in with th.e grid even for larger catches of saithe. the aft belly. Fish. Res. 13:335-352. The saithe did not seem to panic when concen- trated in the bunt even in quantities of up to Larsen, R.B., and B. Isaksen, 1993, Size selectivi- about 20 tons. ty of rigid sorting grids in bottom trawls for The fundamental issue regarding the use of Atlantic cod Gadus morhua! and haddock rigid sorting grids for size selection in purse Melanogrammus aeglefinus!. ICES Mar. Sci, seines is the survival rate of the escaped fish. The Symp; 196;178-182. mackerel and saithe grids allowed the fish to swim out between the bars and escape. It is possi- Lockwood, S., M.G. Pawson, and D,R. Eaton. ble that the selection process exposes the escap- 1983. The effects of crowding on mackerel ing fish to physical stress or injuries that lead to Scomber scombrus!, Physical condition and long-term mortality. Lockwood et al. 983! found mortality, Fish. Res. 2:129-147. that mackerel suffered high mortality when stressed in small net pens, Our preliminary re- Misund, O.A. and Beltestad, A,K, 1994. Size se- sults may indicate that about 60% of the macker- lection of mackerel and saithe in purse seines. el escaping through the grid survive, However, ICES C.M. 1994/B;28, Ref. G, H. 12 pp. further trials to test the survival rates of macker- el that escaped through sorting grids in purse Misund, O.A., W. Dickson, and A. K, Beltestad. seines need to be conducted before any definite 1992. Optiinization of purse seines by large- conclusions about the survival of escaped fish can meshed section and low lead weight. Theoreti- be drawn. cal considerations, sinking speed The saithe seemed to tolerate the selection measurements and fishing trials. Fish. Res. process much better than mackerel, and all the 14:305-317. saithe survived the selection process, Rigid grids may therefore be recommended as a method for Misund, O,A,, and R. Skeide. 1992. Grid-sorting size selection in the purse seine fishery for saithe, of penned saithe. ICES C.M. 1992/B;11 5 pp.