Shark Depredation and Unwanted Bycatch in Pelagic Longline

More documents

Recommendations

Info

Shark Depredation and Unwanted Bycatch in Pelagic Longline Fisheries Almost all respondents indicated that they always retain sharks. Only 34% indicated that they release small sharks. Hooks from small sharks are almost always removed manually once the shark is on board. Four respondents (10%) mentioned that if the hook is not in the mouth then the animals are killed and retained. Almost two-thirds of respondents reported that sharks will either break the main line or bite through the nylon monofilament in the branch line (thus losing hooks as well). The average cost reported from damage and loss of gear to sharks is $11 on a typical mahi mahi set. Fishermen reported having an average of 7.5 mahi mahi damaged from shark bites on a typical longline set. This represents a loss of approximately $30 per trip depending on the size of the fish that are damaged. However, eight (19%) respondents replied that no mahi mahi are damaged by sharks in their typical sets, and that sea lions Otaria byronia and giant squids Dosidiscus gigas are the species responsible for most damage to target catch. Over a third of respondents reported that shark interactions are a problem more because of the amount of time they have to spend to repair and replace loss of gear versus 21% who reported that the cost of lost and damaged gear were the main reason shark interactions are a problem. Another 21% of respondents replied that shark damage is a problem both in terms of time and cost. Only five respondents (12%) reported that neither time nor cost resulting from shark interactions was problematic. Reasons for this response were that (i) repairing and replacing lost gear is fast, (ii) loss of gear by sharks is considered part of their work, and (iii) revenue from shark exceeds the cost of catching them. Almost two thirds (60%) of interviewed fishermen would not avoid catching sharks if they could. The most cited reasons for this response were (i) that shark captures mean extra revenue because of their meat and high value fins, and (ii) that there is nothing to be done to avoid catching sharks since even when using monofilament nylon branch lines sharks are retained. More than one-third (38%) of respondents stated that they would avoid catching sharks because fishing for mahi mahi is more profitable during summer or for purposes of shark conservation (stating that summer time should be considered a temporal ban where they would let sharks reproduce). However, most (83%) of the interviewed fishers replied they would rather not avoid catching sharks because it is, in the end, more profitable for them. Some respondents also indicated that they reconfigure their gear to catch more sharks even before the start of a shark season. A6.9. Methods for Onboard Processing of Retained Sharks Sharks that will be retained and landed are usually not finned. Animals are brought on board where they are immobilized. Sixtyfour percent of respondents indicated that they immobilize the animal by cutting off the tip of the snout and passing a metal wire into the brain. Some respondents (12%) stated that they use a wooden stick to immobilize sharks by hitting them in the snout/head. Over half of them mentioned they would only use the wooden stick for mako sharks and the metal wire for blue sharks. After immobilization the animal is gutted, the head and tail are removed, and the animal is put on ice with the rest of the retained fish. Three (7%) respondents mentioned that they would place viscera and heads in a bag to be discarded at the end of the haul because they believe offal “would scare sharks away”. Finning of animals typically occurs at the port. A6.10. Reasons for Discarding Sharks Despite regulations of minimum size of capture for some shark species, most fishermen (93%) do not discard any shark once it is hooked. Some fishermen (34%) reported that they discard sharks below 40-60 cm in length and only if they are alive when they are hauled to the vessel. The other fishermen (66%) report not discarding any sharks. Two fishermen reported that they do not retain any sharks – one because sharks contaminate the catch of mahi mahi, and the other because of the risk of getting injured from bites while hauling sharks aboard. Shark meat and fins are marketable for several species (blue, mako, hammerhead, porbeagle and other Carcharinidae) and prices are generally equal to or higher than that of the target species mahi mahi. This high value for incidental shark take means that fishers will not discard incidentally captured sharks. Boat space for sharks is not considered a problem and fishermen retain sharks even during the first sets of a fishing trip. Less space for target species means only coming back early to the port. Sharks are preserved on ice covered with paper wrap and placed separate from target species to avoid contamination. A6.11. Practices Employed to Reduce Shark Capture and Depredation Respondents identified employing several strategies to reduce shark capture and depredation. These strategies are practiced to increase mahi mahi capture, and are not necessarily intended to reduce shark capture. The most commonly identified practice to avoid shark interactions is by changing fishing position. During mahi mahi season fishing areas are closer to shore than those areas fished during shark season. Over half (52%) of fishermen interviewed indicated that they would change fishing position in order to reduce gear loss if the catch of sharks was especially high. Another 33% of respondents indicated that they would remain in the fishing zone. Three fishers indicated, particularly toward the end of the mahi mahi season, that they would change monofilament lines for wire cables. The purpose of the gear change would be to increase shark retention, not to reduce gear loss. Wire leaders are not used during the peak of the mahi mahi season because fishermen believe it reduces target species capture. A6.12. Reasons for Discontinuing any Methods Attempted to Reduce Shark Interactions No fisherman has tried or heard of any methods to reduce shark interactions. Only one fisherman responded that he would change the fishing area to catch fewer sharks. 108
Peru Artisanal Mahimahi And Shark Longline Fishery A6.13. Perceptions on Efficacy and Commercial Viability of Strategies to Reduce Shark Interactions A6.13.1. Avoiding peak areas and times of shark abundance Almost two thirds (64%) of respondents believe that shark catch rates will be highest in certain areas which are different from those of the target species. Half of respondents (50%) believe that it is possible to avoid peak areas and times of shark abundance. One third (33%) of respondents believe this is not possible because shark capture is more profitable and they would rather capture sharks if they encounter areas of high shark abundance. This was not the common view, however, because during the summer mahi mahi are more abundant and easily available. A6.13.2. Reducing the detection of baited hooks by sharks, such as by refraining from chumming during the set and not discarding offal and spent bait during the haul About half of respondents (48%) do not believe that refraining from chumming during the set and refraining from discarding offal and spent bait during the haul will reduce shark depredation and bycatch. Thirty-three percent of respondents believe it may help reduce interactions with shark species. All vessels discard spent bait and offal during the haul, and most respondents believe it would be impractical to retain spent bait and offal to discard at the end of hauling because of the lack of space on the vessels. A6.13.3. Limiting shark access to baited hooks, such as altering fishing practices to consider deployment depth of hooks and timing of the soak and haul to avoid problematic shark species Almost half (46%) of respondents believe that it is possible to reduce shark interactions by setting baited hooks shallower or reducing soaking time. Another 43% of respondents believe it is not possible because they still have shark interactions when setting baited hooks shallower. During mahi mahi season, baited hooks are set as deep as 6 fathoms whereas during shark season hooks are set as deep as 11 fathoms. None of the respondents mentioned setting baited hooks deeper because it would reduce their catch rate of target species. A6.13.4. Deterring sharks such as with chemical shark deterrents and electrical deterrents Only 17% of respondents believe that deterrents such as chemical compounds and electrical currents will be effective at reducing shark bycatch and depredation. Another 14% of respondents replied that they did not know of these deterrents or if they would be effective. Over half (62%) of respondents believe that using shark deterrents would not be feasible since they want to capture them due to their high economical value. Respondents (17%) who replied that these deterrents may work mentioned that they would probably be too expensive to use. Some respondents (14%) replied that shark capture is not a problem for them, but, rather, an economic benefit. A6.13.5. Reducing the attractiveness of baited hooks to sharks, such as by using artificial baits, using or not using light sticks, or avoiding a bait type known to result in high shark catch rates Over a quarter (29%) of respondents believe that avoiding bait types known to result in high shark catch rates would reduce shark interactions. About half (43%) of respondents replied that these strategies would not be effective since shark interactions occur even when not using bait types typically employed for shark capture. Of these, four respondents (10%) believe artificial bait would not be economically viable for mahi mahi capture since bait type for this target species is captured fresh before the setting of the longline. Seven respondents (17%) replied that they do not know if these strategies would be effective. One respondent replied that he had used artificial bait but still had shark interactions. A6.13.6. Reducing injury to hooked sharks that you will discard Over a third (34%) of respondents discard live sharks below 40-60 cm in length. Some respondents (7.1%) noted that small sharks that are to be discarded are easy to dehook. If the shark is hooked in the mouth this can be done manually without using any tools. If a shark is small but has swallowed the hook it will be killed and retained. These respondents also believe that the use of dehookers could reduce injury to hooked sharks that are to be discarded. One respondent replied that with training he could use dehookers. Most respondents had not heard of or knew about dehookers. Two respondents replied that they used dehookers to recover hooks but that they did this once the sharks were on board and dead. A6.13.7. Reducing shark retention by avoiding a specific size or type of hook, or by not using wire leaders on branch lines Only one respondent (4.2%) replied that the size of the hook would affect the shark catch rate. Most respondents (69%) replied that shark retention is reduced by not using a wire leader on their branch lines. Respondents use nylon monofilament only because they believe that using wire leaders would decrease their target species capture during the summer. Wire leaders are used during shark season to increase shark capture. A6.13.8. Will the economic impact of sharks be reduced from using a wire leader on branch lines Most respondents believe that the economic impact of sharks would be reduced by using a wire leader on branch lines. Even though most of them find it economically beneficial to capture sharks, they will not switch to using a wire leader because it would reduce mahi mahi capture which is more abundant and easily available at summer time. A6.13.9. What is the most important factor that affects shark CPUE – altering fishing position in relation to certain water temperature, topographic features, or oceanographic features; changing the time of day or month of setting or hauling; changing the depth of hooks, or a combination of these factors? Thirty-eight percent of respondents believe that altering fishing position in relation to certain water temperatures alone will result in 109
Page 3 and 4:
Shark Depredation and Unwanted Byca
Page 5:
Page 9 and 10:
Contents Summary and Conclusions 1
Page 11 and 12:
Contents Appendix 3. Fiji Pelagic L
Page 13:
Contents Appendix 8. USA Hawaii Lon
Page 16 and 17:
Page 19 and 20:
Chapter 1 Introduction and Methods
Page 21 and 22:
Introduction and Methods 1.2. Metho
Page 23 and 24:
Fishing Gear and Operational Charac
Page 25 and 26:
Fishing Gear and Operational Charac
Page 27 and 28:
Shark Catch Rates and Disposition T
Page 29 and 30:
Chapter 4 National and Internationa
Page 31 and 32:
National and International Measures
Page 33 and 34:
Economic, Practical, Ecological and
Page 35 and 36:
Economic, Practical, Ecological and
Page 37 and 38:
Chapter 6 Industry Attitudes and Pr
Page 39 and 40:
Industry Attitudes and Practices Lo
Page 41 and 42:
Industry Attitudes and Practices Fi
Page 43 and 44:
Chapter 7 Potential of Deterrents,
Page 45 and 46:
Potential of Deterrents, Hotspot Av
Page 47 and 48:
References Campana, S.E., L. Marks,
Page 49:
References Neves dos Santos, M., Ga
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73: Shark Depredation and Unwanted Byca
Page 99 and 100: Appendix 5 Japan Pelagic Longline F
Page 101 and 102: Japan Pelagic Longline Fisheries Fi
Page 103 and 104: Japan Pelagic Longline Fisheries mo
Page 105 and 106: Japan Pelagic Longline Fisheries Ta
Page 107 and 108: Japan Pelagic Longline Fisheries is
Page 109 and 110: Japan Pelagic Longline Fisheries ta
Page 111 and 112: Japan Pelagic Longline Fisheries In
Page 113 and 114: Japan Pelagic Longline Fisheries A5
Page 115 and 116: Appendix 6 Peru Artisanal Mahimahi
Page 117 and 118: Peru Artisanal Mahimahi And Shark L
Page 121: Peru Artisanal Mahimahi And Shark L
Page 127 and 128: Appendix 7 South Africa Pelagic Lon
Page 129 and 130: South Africa Pelagic Longline Tuna
Page 135 and 136: Appendix 8 USA Hawaii-based Pelagic
Page 137 and 138: USA Hawaii-based Pelagic Longline S
Page 147 and 148: Appendix 9 USA Atlantic, Gulf of Me
Page 149 and 150: USA Atlantic, Gulf of Mexico and Ca
show all

Shark Depredation and Unwanted Bycatch in Pelagic Longline

Create successful ePaper yourself

Delete template?

Save as template?