Capture Of Seabirds Research Articles

Mitigation of seabird bycatch in New Zealand squid trawl fisheries provides hope for ongoing solutions

ABSTRACT Although there is an increasing awareness of the high rates of seabird bycatch in trawl fisheries globally, there is relatively limited implementation of effective mitigation measures. Seabirds that are attracted to the stern of the trawl vessel to feed on fish-waste can be drowned or injured when they collide with warps/cables or when they become entangled in nets. Managing fish-waste discharge (processing offal and discards) and limiting access to it by scaring birds have been identified as the most effective measures to reduce seabird mortality from collisions with warps. New Zealand’s arrow squid (Nototodarus spp.) trawl fishery occurs during the austral summer and autumn when there is significant overlap with large numbers of foraging seabirds due to the proximity of breeding areas. Regulations introduced by the New Zealand government in 2007 requiring the use of devices to reduce warp strikes and operational procedures to manage fish-waste were independently implemented by the fishing industry in 2007 with the support of fishery regulators. The rate of capture of albatrosses by warps decreased from a mean of 2.9 birds per 100 tows during the period 2003 to 2006 to a mean of 0.7 birds per 100 tows after 2007. Long-term ownership of squid fishery quota catalysed the proactive engagement of the industry and has been reflected in a positive cultural shift in the attitude of fishers towards managing the risk of the capture of seabirds. Multi-sector collaboration and engagement allowed for the translation of experimental mitigation results into long-term, industrial-scale operational practices.

Incidental capture of seabirds in Argentinean side-haul trawlers

SummaryBetween April 2008 and July 2015, we conducted a total of 18 trips on five different side-haul trawlers fishing within the Argentine Exclusive Economic Zone, monitoring 486 hauls. We observed 100% of the hauls and monitored trawl cables for 136.7 hours, about 5% of the trawl effort, to identify the levels of seabird bycatch from net entanglements and collisions with trawl cables. A total of 35 net entanglements of White-chinned Petrels Procellaria aequinoctialis, Great Shearwaters Ardenna gravis, Black-browed Albatrosses Thalassarche melanophris and Southern Royal Albatross Diomedea epomophora were recorded, all of which occurred during the autumn and winter. Additionally, 656 seabird collisions against trawl cables were recorded including 39 heavy, 96 medium and 521 light. Further, we recorded nine Black-browed Albatrosses and two Great Shearwaters potentially dead. Although in the study fishery the number of deaths in the trawl cables could surpass the number of birds incidentally killed in nets, the mortality rate caused by the latter type of interaction far exceeds those observed in nets from other trawl fisheries operating in the Patagonian Shelf. Fortunately, 26% of the seabirds entangled in the net were recovered and released alive, which indicates that awareness and training in safe bird handling and release may improve captured seabird survival rates. The main objectives of this work is to highlight a little-studied source of seabird mortality by entanglement, to generate discussion on potential technical mitigation measures for side-haul trawl fisheries, and to propose crew training in safe handling and release of seabirds as an immediate mitigation measure.

Illuminating gillnets to save seabirds and the potential for multi-taxa bycatch mitigation

Bycatch in net fisheries is recognized as a major source of mortality for many marine species, including seabirds. Few mitigation solutions, however, have been identified. We assessed the effectiveness of illuminating fishing nets with green light emitting diodes (LEDs) to reduce the incidental capture of seabirds. Experiments were conducted in the demersal, set gillnet fishery of Constante, Peru and compared 114 pairs of control and illuminated nets. We observed captures of a total of 45 guanay cormorants (Phalacrocorax bougainvillii), with 39 caught in control nets and six caught in illuminated nets. Seabird bycatch in terms of catch-per-unit-effort was significantly (p < 0.05) higher in control nets than in illuminated nets, representing an 85.1% decline in the cormorant bycatch rate. This study, showing that net illumination reduces seabird bycatch and previous studies showing reductions in sea turtle bycatch without reducing target catch, indicates that net illumination can be an effective multi-taxa bycatch mitigation technique. This finding has broad implications for bycatch mitigation in net fisheries given LED technology's relatively low cost, the global ubiquity of net fisheries and the current paucity of bycatch mitigation solutions.

Catch, effort and fishing practices in a recreational gillnet fishery: Assessing the impacts and response to management change

Gillnets are typically considered to be a commercial fishing gear yet their use by recreational fishers is permitted in several developed countries, often with few if any restrictions on the total number of users. Despite this there have been very few attempts to assess the impacts of recreational gillnet fisheries both in terms of harvest and implications for bycatch. Recreational gillnetting has a long history in Tasmania, Australia, and over the past two decades the fishery has been the focus of a number of management measures to improve fishing practices. In this study, the fishing activity of recreational gillnet license-holders was monitored for 12-months using a telephone-diary based panel survey. Catch, effort and fishing practices were compared with previous recreational fishing surveys and the commercial fishery. During 2010 an estimated 6600 recreational license-holders used gillnets, accounting for 25,712 (95%CI 22,142–28,901) net-days of effort and a total catch of 173,922 (95%CI 147,165–202,950) marine organisms, 35.5% of which were discarded. The recreational fishery is comprised of two main sub-fisheries, a mixed reef-fish fishery and a fishery for marine farm escapees. Four species, three representing key target species and one primarily a bycatch species, accounted for just over half of the total gillnet catch by number. The harvested component of the recreational gillnet catch was comparable to or exceeded commercial landings for the key species, highlighting the importance of taking account of the recreational fishery in stock assessments and species management. Despite an increase in the number of gillnet license-holders, recreational gillnet effort in Tasmania has halved since the late 1990s. This decline in effort appears to be linked to the greater regulation of fishing practices as well as reduced availability of two key target species, one of which has been classified as over-fished. Although recreational fishing practices have improved, the impacts on target and non-target species, including the incidental capture of seabirds and survival of bycatch, remain issues for concern.

Best practices to mitigate seabird bycatch in longline, trawl and gillnet fisheries—efficiency and practical applicability

Growing concerns have been raised about incidental capture of seabirds in various fisheries. Here, studies testing measures to prevent seabird bycatch in longline, trawl and gillnet fisheries are reviewed in order to identify the most efficient mitigation methods. There is potential for considerable reduction in mortality rates in most longline fisheries because effective measures have been developed. However, there is no single solution as the efficiency of a measure is specific to each fishery. In demersal longline fisheries where northern fulmar is the dominant seabird captured, streamer lines have been proven to virtually eliminate mortality. In the fishery for Patagonian toothfish where interactions with albatrosses occur, night setting has resulted in considerable bycatch reductions. Night setting has also been proven to be efficient in pelagic fisheries, but this measure should be used in combination with streamer lines and weighted longlines in areas inhabited by nocturnal and diving birds. The main cause of mortality in trawl fisheries is collision with warp and netsonde cables, but studies are fragmentary. Interactions between cables and seabirds have been shown to be rare at times of no offal discharge, suggesting that a no-discharge policy would virtually eliminate mortality. Streamer lines have been proven to effectively reduce cable strikes under offal discharge. Measures to prevent birds from diving into the trawl net meshes have not been tested. Efficient mitigation methods that maintain target fish catch still have to be identified for gillnet fisheries. Future research in longline fisheries should fine-tune the most promising measures for each specific fishery. Effective measures identified for trawl fisheries need to be expanded to and tested in other areas where seabird interactions occur.

Comparing factors associated with total and dead sooty shearwater bycatch in New Zealand trawl fisheries

Incidental capture of seabirds is a conservation concern because such periodic ‘bycatch’ may cause population declines. Not all birds die upon capture, but distinctions between total and dead captures are rarely done. Thus, it is currently unclear whether using total captures is an adequate simplification, for example when studying factors associated with bycatch. We investigated this question by analysing total and dead procellariiform seabird captures of 663 trawling operations between 1996 and 2008 in the Exclusive Economic Zone of New Zealand. As potential factors associated with bycatch, we considered eleven technical and seven environmental characteristics recorded by onboard observers during commercial trawling. A total of 1 231 procellariids were recovered as bycatch, with sooty shearwaters ( Puffinus griseus) comprising 98% of the bycatch sample. Our analyses indicated that specific technical (headline height) and environmental factors (month, daylight, sea state, area code) influenced both total and dead captures of sooty shearwaters, with similar results for both response variables. Using total captures may thus be an adequate simplification in the interpretation of sooty shearwater captures in New Zealand trawl fisheries, and practices that mitigate the overall capture of birds will be most effective.

Combined impacts of longline fisheries and climate on the persistence of the Amsterdam Albatross Diomedia amsterdamensis

Incidental capture of seabirds in longline fishing gear is a central issue in the conservation of many long‐lived marine species. Despite growing evidence of climate‐induced effects on population trends of long‐lived species, climate change remains generally overlooked in most risk assessments of seabirds. Because variation in climate may interact with the detrimental effects of bycatch, considering climate is of great importance, especially in the context of ongoing global warming. This paper examines the combined effects of bycatch and climate change on the persistence of one of the world’s rarest birds, the Amsterdam Albatross Diomedea amsterdamensis, which has a single population in the upland plateau of Amsterdam Island (Southeast Indian Ocean). Using continuous monitoring from 1983 onwards, we first estimated the relationship between climate and the species’ demographic parameters. We then built a stochastic matrix population model to estimate the population growth rate and the probability that the population declines below the level recorded in 1983 of nine breeding pairs under different scenarios involving the joint effects of additional mortality caused by longline fisheries and climate change. The results suggest that the demography of the Amsterdam Albatross is influenced by climate in both breeding and wintering grounds and that these relationships may to some extent compensate for the impact of additive bycatch mortality. However, these compensatory effects would be negligible if the annual additional mortality exceeds around six individuals per year, suggesting that the resumption of longline fishery in the foraging range of the Amsterdam Albatross would rapidly put this species at risk of extinction.

The incidental capture of seabirds by Spanish drifting longline fisheries in the western Mediterranean Sea

The western Mediterranean Sea is an important fishing area for the Spanish drifting longline fleet, targeting swordfish ( Xiphias gladius ), bluefin tuna ( Thunnus thynnus ) and albacore ( T. alalunga ). Some seabird species can be captured incidentally as bycatch marine fauna. From July 1999 to August 2000 information on 554 surface longline sets was collected by onboard observers of the Spanish Oceanographic Institute (IEO) on 18 longline fishing boats working within the Spanish Mediterranean fishing area. Eleven yellow-legged gulls ( Larus cachinnans ), 9 Cory´s shearwaters ( Calonectris diomedea ) and 1 Northern gannet ( Morus bassanus ) were captured incidentally. Bycatch rates ranged from 0.002 to 0.023 birds/1000 hooks.

Seabird by-catch and bait loss in long-lining using different setting methods

Seabirds taking baits during long-line setting occasionally become caught and are killed, while the associated bait-loss may have serious impact on long-lining efficiency and profitability. Two different setting methods were tested as a solution to this problem in the autoline fishery in the north Atlantic; lines were set either through a setting funnel that guided the baited line beneath the surface or a seabird scaring device was used. Bait loss and the catches of target species and seabirds were compared with and without such methods. Accidental catches of birds were reduced by both methods, most effectively by the seabird scarer. Losses of mackerel bait were also significantly reduced by using the scarer, but not by using the setting funnel. No increase in the catches of target species was demonstrated by using either of the setting methods. However, bait loss caused by seabirds was regarded as a minor problem in this fishing experiment. Suggestions on how to improve the efficiency of the two methods are discussed, and a combination of these methods is proposed as a method to reduce greatly the incidental capture of seabirds in the autoline fishery in the north Atlantic.

Interactions between longline vessels and seabirds in Kerguelen waters and a method to reduce seabird mortality

A longline fishery for Dissostichus eleginoides has recently developed in the vicinity of South Georgia and Kerguelen islands, two internationally important breeding areas for procellariiform birds. The number of hooked birds and a method to reduce mortality were investigated during 13 days of fishing activity in Kerguelen waters in February 1994. Between 100 and 600 seabirds were always observed behind the longline vessel during daytime. The main ship-following species were the white-chinned petrel Procellaria aequinoctialis (67% of counts), giant petrels Macronectes spp. (8%) and the wandering albatross Diomedea exulans (11%), black-browed albatross D. melanophris (6%) and grey-headed albatross D. chrysostoma (2%). Only diving species were caught on the lines, i.e. the white-chinned petrel ( n = 36) and the grey-headed albatross ( n = 2). Marked differences in the mortality rate were observed between day and night (1·00 versus 0·38 birds per 1000 hooks), and at night when the decklights were on or off (0·59 versus 0·15 birds per 1000 hooks). Dumping of homogenized offal during line settings greatly reduced incidental capture of seabirds, mainly because birds were more attracted by offal than by hooked baits. We therefore propose that the dumping of offal during line settings should be included in the regulations of the longline fishery for Dissostichus in order to minimize seabird mortality.

Corrigenda

Volume 3 Number 3, Murray et al., Incidental capture of seabirds by Japanese southern bluefin tuna longline vessels in New Zealand waters, 1988-1992: on p. 201, second paragraph, the sentence beginning On Adams Island should read:

Incidental Capture of seabirds by Japanese southern bluefin tuna longline vessels in New Zealand waters, 1988-1992

SummaryFishery observers recorded incidental capture of seabirds during 785 days on Japanese bluefin tuna longline vessels around New Zealand between April and August each year, 1988-1992. High numbers of albatrosses Diomedea spp. and petrels Procellaria spp. were caught on longline hooks during setting and drowned. Twelve seabird taxa were recorded, six of them breeding only in New Zealand. Most were breeding adults, except for Grey-headed and Black-browed Albatrosses. No bias in sex ratio was evident except for Grey Petrels, of which nearly all were female. Winter-breeding species were most often caught. Birds were not caught randomly, but in a highly aggregated fashion suggestive of complex behavioural interactions with the fishery. Most albatrosses were caught by day in the south whereas most petrels were caught by night north-east of New Zealand. Highest capture rates occurred at dawn and dusk off north-east New Zealand in June-August. Very large catches at specific sites contributed disproportionately to the overall catch rate. The estimated minimum number of total seabirds caught in New Zealand waters declined from 3,652 in 1988 to 360 in 1992, probably as a result of mitigation measures introduced progressively by the industry and by government regulation. Use of tori lines to prevent birds seizing baits had an effect, as did setting in total darkness in the south. Considerably more work needs to be done on the development of improved mitigation measures. Greater observer coverage is required to measure accurately the mortality of individual seabird species on tuna longlines throughout the Southern Ocean and to determine the effectiveness of mitigation measures.

Incidental capture of seabirds in the New Zealand subantarctic squid trawl fishery, 1990: J. A. Bartle, Bird Conservation International, 1(4), 1991, pp 351–359

Incidental capture of seabirds in the New Zealand subantarctic squid trawl fishery, 1990: J. A. Bartle, Bird Conservation International, 1(4), 1991, pp 351–359

Incidental capture of seabirds in the New Zealand subantarctic squid trawl fishery, 1990

SummaryFisheries observers recorded incidental capture of seabirds during 338 days on Soviet squid trawlers in New Zealand subantarctic shelf waters around the Snares and Auckland Islands in 1990. Seven species were recorded entangled in fishing gear, including very high numbers of breeding adult White-capped Albatrosses Diomedea cauta steadi. The actual level of White-capped Albatross mortality was estimated at 2,300 birds in 1990, and is not considered sustainable. Nearly all albatrosses were killed by collision with the netsonde monitor cable. In New Zealand waters this equipment is carried only by Soviet trawlers, and is considered obsolete. Replacement of this cable by discrete netsonde transducers on Soviet trawlers should be a global seabird conservation priority.