By-catch of common minke whales (<i>Balaenoptera acutorostrata</i>) in Norwegian demersal trawl and longline fisheries, 2011–2020

The implementation of ACAP Best Practice Advice to mitigate seabird bycatch in fisheries: Issues and options

Seabird bycatch in fisheries, and the development of effective mitigation to minimize this, have been subject to increasing research attention over the past three to four decades. Trawl fisheries represent a particular challenge, as bird mortalities (especially highly threatened albatrosses and large petrels, Procellariforms) occur primarily through difficult-to-detect collisions with warp and net monitoring cables. Effectiveness of bird-scaring lines (BSLs) as a mitigation measure can be fleet-specific, and studies relating specifically to reducing collisions with the net monitoring cable are rare. To support improved assessment and mitigation of seabird bycatch in trawl fisheries, we studied the mortality associated with mid-water and bottom factory trawl vessels along the southern tip of the Argentine Patagonian shelf, across 2144 trawls from 2012 to 2019, with three specific objectives: (i) inform improved bycatch management in this (and other) trawl fisheries by analysing differences in seabird collision rates and outcomes between net monitoring and warp cables, as well as the effect of mitigation measures in reducing collisions; (ii) explore the effects of key fishing operation variables on seabird impact outcomes; and (iii) estimate the annual seabird mortality in the study fleet. We tested the efficacy of BSLs as a mitigation measure to reduce seabird mortality, on warps and net monitoring cables. Our results show that seabird mortality increases in the presence of a net monitoring cable. Our estimation of fishery-wide mortality without the use of BSLs includes 108 [31–186] Southern royal albatross (Diomedea epomophora) and 279 [108–465] Black-browed albatross (Thalassarche melanophris) killed annually by the collisions with the net monitoring cable. We demonstrate the efficacy of BSLs in reducing the number of collisions and in combination with no discarding of fishes, seabird interactions fell to c. zero. Our study builds the case for better bycatch data collection in trawl fisheries, the strong influence of discarding, and the feasibility of simple mitigation measures to reduce seabird bycatch, including on the net monitoring cable.

Spatial segregation in at-sea distribution is frequently observed in seabirds and can have important implications for conservation and management. Globally, many albatross and petrel populations are declining due to bycatch in fisheries. In South Georgia, the decrease in wandering albatrosses (Diomedea exulans) differs among breeding sites, which could reflect segregation in foraging areas, leading to differing degrees of overlap with particular fishing fleets and hence unequal bycatch risk. We investigated whether spatial segregation could explain the different rates of population decline of wandering albatrosses at South Georgia. We tracked wandering albatrosses from 2 breeding sites at South Georgia, Prion Island, and Bird Island, located 50km apart. We investigated potential causes of spatial segregation with species distribution models and by comparing wind conditions among sites. Overlap with fisheries was quantified for each population. Although overall distributions were from the Antarctic to the subtropics, virtually all wandering albatrosses from Bird Island foraged only to the west of the island group, whereas those from Prion Island foraged to the east and west. Preferred habitat characteristics were similar at both colonies, and waters to the east and west provided foraging habitat. Wind conditions when birds departed were also similar at the 2 sites. Because neither habitat specialization nor wind conditions appeared to be factors in the observed spatial segregation among colonies, this segregation likely reflected a combination of past experience, information exchange, and cultural evolution. Breeding birds from both sites overlapped most with Chinese squid jiggers, Argentinian trawlers, and South Korean set (demersal) longliners, but the spatial segregation led to a higher overlap with demersal longline, demersal trawl, and pelagic longline fisheries by wandering albatrosses at Bird Island, which could have resulted in the faster population decline. Ours is one of the first studies to demonstrate how spatial segregation may affect population dynamics, which has important implications for the conservation of this globally threatened species.

Bycatch of short-beaked common dolphin (Delphinus delphis) in the pair bottom trawl fishery of the Bay of Biscay and its mitigation with an active acoustic deterrent device (pinger)

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.

Reducing flatfish bycatch in roundfish fisheries

Reduction in seabird mortality in Namibian fisheries following the introduction of bycatch regulation

Worldwide, incidental bycatch in fisheries is a conservation threat to many seabird species. Although knowledge on bycatch of seabirds has increased in the last decade, most stems from longline fisheries and the impacts of coastal gillnet fisheries are poorly understood. Gillnet fishing for North Atlantic lumpsucker (Cyclopterus lumpus) is one such fishery. We collated and synthesized the available information on seabird bycatch in lumpsucker gillnet fisheries across the entire geographical range to estimate and infer the magnitude of their impact on the affected seabird populations. Most birds killed were diving ducks, cormorants and auks, and each year locally high numbers of seabirds were taken as bycatch. We found large differences in bycatch rates among countries. The estimated mean bycatch in Iceland was 2.43 birds/trip, while the estimates in Norway was 0.44 and 0.39 birds/trip, respectively. The large disparities between estimates might reflect large spatial differences in bycatch rates, but could partly also arise due to distinctions in data recorded by onboard inspectors (Iceland), self-administered registration (Norway) and direct observations by cameras (Denmark). We show that lumpsucker gillnet fisheries might pose a significant risk to some populations of diving seabirds. However, a distinct data deficiency on seabird bycatch in terms of spatio-temporal coverage and the age and origins of the birds killed, limited our abilities to fully assess the extent and population consequences of the bycatch. Our results highlight the need for a joint effort among countries to standardize monitoring methods to better document the impact of these fisheries on seabirds.

Bycatch of seabirds in offshore commercial fisheries has long been recognized as a serious conservation issue (e.g. Brothers, 1991; Brothers, Cooper & Lokkeborg, 1999), but until recently the problem was principally associated with industrial longline gear. In fact, pelagic seabird bycatch is very much a multi-gear problem. Watkins, Petersen & Ryan (2008) have presented the latest in a string of recent case studies documenting geographically widespread and sometimes severe levels of seabird bycatch in industrial trawl fisheries throughout the Southern Hemisphere (Weimerskirch, Capdeville & Duhamel, 2000; Sullivan, Reid & Bugoni, 2006a; Baker et al., 2007; Gonzales-Zevallos, Yorio & Caille, 2007). Substantial seabird bycatch occurs in trawl fleets of the Northern Hemisphere as well (e.g. in Alaskan trawl fisheries for groundfishes; NMFS, 2006). The issue is one of global importance that requires urgent international attention. National and international fisheries management bodies face several challenges as they move forward to address seabird bycatch within a multi-gear context. One fundamental question is what is the relative and cumulative threat to seabird populations from bycatch in trawl and longline gear? Answering this question depends on having reasonable estimates of mortality from these two gear types across the multitude of international fishing fleets with which particular seabird populations interact (e.g. Baker et al., 2007). This will require that new observer programs be established for national trawl fleets that interact with seabirds in their waters, and that international programs currently working to quantify seabird bycatch in high-seas longline fisheries (see Gilman & Moth-Poulsen, 2007) expand to quantify threats posed by trawl fisheries as well. Trawl gear poses a particularly difficult challenge for seabird bycatch estimation because a large but often unquantified proportion of birds killed by interactions with trawl cables (the dominant cause of mortality in trawl gears) is not hauled onto the vessel and therefore goes unobserved by traditional observer-data collection protocols (e.g. Gonzales-Zevallos & Yorio, 2006; Sullivan et al., 2006a). Watkins et al. (2008) observed that only two out of the 30 known seabird fatalities from cable interaction were eventually hauled aboard, corresponding at best to an overall 0.067 ( 0.046 binomial SE) detection rate for this type of mortality if only haul data had been used to estimated bycatch. This indicates the need to update observer protocols of seabird bycatch monitoring in trawl fisheries, to ensure proper accounting of bird mortalities resulting from cable collisions. Alternative methods for monitoring seabird bycatch in trawl fisheries should also be explored, as observer programs appropriate for monitoring seabird–trawl cable interactions are labor intensive and therefore expensive. Watkins et al. (2008) were only able to observe 0.5% of annual trawl fishing effort for this reason, and even some of the most well-funded fishery observer programs in the world (e.g. several in the United States) are too overstretched financially to meet observer coverage goals (Rossman, 2007). One promising approach is video monitoring (McElderry et al., 2004; Ames, Williams & Fitzgerald, 2005), which Watkins et al. (2008) used with apparent success during the first part of their study. Another strategy may be to augment traditional observer-data collection protocols, which are based on sampling hauled-in bycatch, over the long term with shorter intensive studies aimed at estimating species composition and non-detection rates for seabirds killed by cable interactions that are not retrieved during hauling of gear. These might then be applied as correction factors to statistically estimate actual seabird bycatch in trawls from data collected using conventional observer protocols. To our knowledge, Watkins et al. (2008) were the first to provide some empirical inference about the rate of bycatch non-detection in trawl fisheries and we encourage future studies to report similar data and estimates. As research and management programs respond to increase collection of trawl bycatch data, it would be helpful to adopt common metrics for reporting trawl bycatch. Watkins et al. (2008) reported bycatch per trawl hour, which

A common definition of the term ‘bycatch’ is that part of the gross catch which is captured incidentally to the species towards which there is directed effort. Under such a definition, there are few fisheries in Australia (nor the world) which do not have bycatch, making the scope, diversity and history of the issue enormous. In recent years, the majority of interest in bycatch has focused on demersal trawl fisheries because conventional otter trawls are comparatively non-selective fishing gears and so catch large quantities of a wide range of untargeted species.

Assessment of relative performance of a square-mesh codend design across multiple vessels in a demersal trawl fishery

Impact of ground gear design on catch efficiency in demersal trawl fishery

Fisheries bycatch is a threatening process for populations of procellariiform seabirds, and is of particular importance for the conservation of albatross, an especially threatened group at a global scale. There is a high level ofendemism of albatross and petrels in New Zealand waters, and around one-third of the world's species of procellariiform seabirds breed in this area. Therefore, understanding the levels of mortality of these species in the New Zealand Exclusive Economic Zone is important for global conservation of the order. For New Zealand fisheries for the 1998-2004 fishing years, we estimated total seabird bycatch using data from scientific observers with model-based estimation procedures. Although sectors of the fishing activity were not evenly covered by observers, we were able to estimate seabird bycatch for large scale fisheries by vessel size (split at 28 m length), season, area and year. Approximately 5500 seabirds (credible interval between 2000 and 10 000) are estimated to be landed in New Zealand trawl and longline fisheries annually, as a result of interactions with fishing gear. Few data were available for the small vessels, thus estimates are highly uncertain. Mortalities are likely to be most common in trawl fisheries at approximately 2000-3000 seabirds annually, with the greatest contribution coming from large vessels. Around one half of these birds were albatross. For large surface longline vessels we estimated that fewer than 500 seabirds were killed annually during the main tuna fishing season. For large demersal vessels, seabird mortality was estimated to have decreased from around 1800 seabirds in 2001 to 600 seabirds in 2004. We report observed captures by species for each fishing method and area for the fishing years 1998-2004. Thirty-one species of Procellariiformes were identified during this period, over half of which are threatened species. For some species, such as White-chinned Petrel, Procellaria aequinoctialis and White-capped Albatross, 1halassarche steadi, several hundred individuals were caught. For 15 species, fewer than 10 individuals were identified. However, the unrepresentative deployment ofobserver coverage across fishery areas makes it difficult to interpret the conservation implications of species captures. A high proportion of the petrel species was observed caught primarily from areas surrounding their breeding sites while albatross were caught across breeding and non-breeding areas. Greatly improved observer sampling ratios, and studies of population status and trends, are needed to understand the conservation implications of the effects of New Zealand trawl and longline fishing mortalities on seabird populations.

BackgroundMinke whales are separated into two genetically distinct species: the Antarctic minke whale found in the southern hemisphere, and the common minke whale which is cosmopolitan. The common minke whale is further divided into three allopatric sub-species found in the North Pacific, southern hemisphere, and the North Atlantic. Here, we aimed to identify the genetic ancestry of a pregnant female minke whale captured in the North Atlantic in 2010, and her fetus, using data from the mtDNA control region, 11 microsatellite loci and a sex determining marker.ResultsAll statistical parameters demonstrated that the mother was a hybrid displaying maternal and paternal contribution from North Atlantic common and Antarctic minke whales respectively. Her female fetus displayed greater genetic similarity to North Atlantic common minke whales than herself, strongly suggesting that the hybrid mother had paired with a North Atlantic common minke whale.ConclusionThis study clearly demonstrates, for the first time, that hybrids between minke whale species may be fertile, and that they can back-cross. Whether contact between these species represents a contemporary event linked with documented recent changes in the Antarctic ecosystem, or has occurred at a low frequency over many years, remains open.

Distribution and abundance of skates (Bathyraja spp.) on the Kerguelen Plateau through the lens of the toothfish fisheries