The broader ecosystem impacts of fishing continue to present a challenge to scientists and resource managers around the world. Bycatch is of greatest concern for marine mammals, for which fishery bycatch and entanglement is the number one cause of direct mortality. Climate change will only add to the challenge, as marine species and fishing practices adapt to a changing environment, creating a dynamic pattern of overlap between fishing and species (both target and bycatch). Economists suggest policy instruments for reducing bycatch that move away from top-down, command-and-control measures (e.g. effort reduction, time/area closures, gear restrictions, bycatch quotas) towards an approach that creates incentives to reduce bycatch (e.g. transferable bycatch allowances, taxes, and other measures). The advantages of this flexible, incentive-oriented approach are even greater in a changing and increasingly variable environment, as regulatory measures would have to be adapted constantly to keep up with climate change. Unlike the regulatory process, individual operators in the fishery sector can make adjustments to their harvesting practices as soon as the incentives for such changes are apparent and inputs or operations can be modified. This paper explores policy measures that create economic incentives not only to reduce marine mammal bycatch, but also to increase compliance and induce technological advances by fishery operators. Economists also suggest exploration of direct economic incentives as have been used in other conservation programs, such as payments for economic services, in an approach that addresses marine mammal bycatch as part of a larger conservation strategy. Expanding the portfolio of mandatory and potentially, voluntary, measures to include novel approaches will provide a broader array of opportunities for successful stewardship of the marine environment.
As tropical pelagic species are attracted by floating objects in the surface of the ocean, industrial purse seiners deploy thousands of man-made drifting fish aggregating devices (DFADs) to facilitate their catch of tunas. However, the sharp increase in the use of DFADs leads to some ecological concerns, such as producing higher amount of by-catch or alteration of natural behaviour of fish. We used fishers’ satellite-linked GPS buoys equipped with echo-sounders to continuously collect acoustic samples under remote DFADs and investigate the diel behaviour patterns of the associated fish (i.e., non-tuna species and small and large tunas) and their potential biological interactions. Results showed a strong correlation between the presence of non-tuna species and small tunas, and between small and large tunas. Diel biomass dynamics were highly variable and seem to be both species and region-specific, which may suggest adaptive behaviour patterns. Tuna associated with DFADs in the Somalia area showed a clear night-time associative behaviour. In contrast, tuna in the NW Seychelles associated with DFADs to a greater degree during daytime. In the Mozambique Channel, large tuna showed daytime associative behaviour, while small tuna showed a maximum biomass at sunrise, decreasing over the day. The associative behaviour of non-tuna species was slightly variable, being uniform near the equator or showing two peaks when increasing latitude. This study shows the importance and effect of biological factors on the associative behaviour of the fish and serves as a first step towards improving pre-set selectivity of purse seine fisheries using DFADs. The fish presence and density may improve DFAD attraction and detectability and the observed periodicity by species and area shows both similarities and differences with published literature.
Discard management needs to draw on scientific research and advice, usually supported by specific statistical modeling analysis. A wide range of statistical analysis methods were applied to fishery data in an attempt to distinguish factors that influence the species discard composition. While such approaches are important, they are still incomplete for disaggregating the economic and spatial-temporal factors for analyzing of this process and obtain a whole view of this issue. Our study aims to fill this gap by identifying, describing, and quantifying factors that influence discards of trawl fisheries using a multivariate approach based on five complementary aspects: “economic”, “vessel characteristics”, “spatial”, “temporal” and “environmental”. In addition, a spatial multi-criteria approach were used to investigate discard hot-spot areas using ecological criteria such as vulnerability and resilience of the discarded species. Using these ecological criteria will concentrate conservation efforts on the most relevant sites minimizing discards of a variety of potentially vulnerable species. This approach was applied to a case study of a multi-species demersal bottom trawl fisheries in north Spain, Cantabrian Sea (ICES area VIIIc). Results showed how spatial and economic factors highly affect species discard composition, identifying specific spatial-temporal discard hot-spots to be preferentially avoided by fishers. Mitigation measures for future fisheries management strategies should be implemented at multiple stages of the discarding process, both in the selection of the fishing grounds and the economic valorization of the discarded species.
The Magnuson-Stevens Fishery Conservation and Management Act (MSA) is the primary law that codifies marine fisheries management in United States federal waters. The MSA was amended in 2006 with Section 610, an international provision that directs the Secretary of Commerce to unilaterally identify foreign nations engaged in the incidental capture (bycatch) of protected living marine resources (PLMRs) under specific conditions. In 2013 the United States identified Mexico for bycatch of a PLMR – the North Pacific loggerhead turtle – representing the first time a nation has been identified for bycatch under section 610. This paper evaluates the initial effects of the identification on loggerhead bycatch management efforts in Mexico and provides policy recommendations for improving the law and its implementation. In the wake of the unilateral identification, Mexico downplayed and denied the bycatch problem that their agencies had previously accepted and cancelled a bycatch research partnership between their federal fisheries science agency and U.S. researchers. Moreover, fishers invested in bycatch reduction and monitoring programs ceased to participate, jeopardizing their understanding of the problem and their co-development of bycatch solutions. However, the identification and subsequent consultation process ultimately resulted in Mexico implementing federal loggerhead bycatch regulations that are temporarily comparable with relevant U.S. measures. These regulations establish a temporary fisheries reserve (authorized for two years) that includes monitoring of bycatch, a loggerhead bycatch mortality cap, temporal and spatial restrictions on fishing gear and practices, and a closure of all finfish fisheries during the summer of 2016. As a result, turtle bycatch was likely substantially reduced in 2016, but at the cost of artisanal fishers' entire seasonal income. Policy recommendations are made, highlighting the need to: 1) better assess the socioeconomic, political, and environmental consequences associated with using the threat of trade sanctions to compel nations to reduce their bycatch; and 2) facilitate a more consistent consideration of bycatch data across nations such that the current policy does not create a disincentive for other nations to assess or report PLMR bycatch.
Fisheries bycatch is a major threat to seabird populations, and understanding sex- and age-biases in bycatch rates is important for assessing population-level impacts. We analysed 44 studies to provide the first global assessment of seabird bycatch by sex and age, and used generalised models to investigate the effects of region and fishing method. Bycatch was highly biased by sex (65% of 123 samples) and age (92% of 114 samples), with the majority of samples skewed towards males and adults. Bycatch of adults and males was higher in subpolar regions, whereas there was a tendency for more immatures and females to be killed in subtropical waters. Fishing method influenced sex- and age-ratios only in subpolar regions. Sex- and age-biases are therefore common features of seabird bycatch in global fisheries that appear to be associated largely with differences in at-sea distributions. This unbalanced mortality influences the extent to which populations are impacted by fisheries, which is a key consideration for at-risk species. We recommend that researchers track individuals of different sex and age classes to improve knowledge of their distribution, relative overlap with vessels, and hence susceptibility to bycatch. This information should then be incorporated in ecological risk assessments of effects of fisheries on vulnerable species. Additionally, data on sex, age and provenance of bycaught birds should be collected by fisheries observers in order to identify regions and fleets where bycatch is more likely to result in population-level impacts, and to improve targeting of bycatch mitigation and monitoring of compliance.
With the observer data from the National Marine Fisheries Service Pelagic Observer Programme (POP) and the logbook data from the US Atlantic pelagic longline fishery, we estimated the seabird bycatch in the fishery during 1992–2012. The POP observed 13 847 longline sets, with a total of 141 seabirds captured on 74 sets. The overall nominal catch rate was 0.0102 birds per set and 0.014 birds per 1000 hooks. We applied a random year effect model (RYEM) for analysis of the whole study region that includes 11 fishing zones. Extrapolating from the observed seabird bycatch, we estimated a total of 2255 seabirds captured on average (coefficient of variation CV = 14.72%) by the total fleet from 1992 to 2012. The highest estimate of seabird bycatch occurred in the middle Atlantic bight (MAB), followed by the northeast coast (NEC). Estimated seabird bycatch, by season, was higher in summer, fall, and winter than in spring. Longline sets targeting a mixed group of species caught the majority of the total seabird bycatch, and longline sets targeting swordfish and tuna also caught more seabirds than those sets targeting other species. To incorporate spatial variation into parameter estimation, allowing parameters to vary spatially, we applied a spatial expansion model (SEM) to data for the three fishing zones with the most observed seabird bycatch, the NEC, the MAB and the south Atlantic bight. When compared with the estimates from the RYEM (145–1049 seabirds with a CV of 16.4–23.5%), the SEM produced higher estimates (155–1489 seabirds) of the total seabird bycatch for each of these areas and a larger CV (19.1–65.4%). The RYEM may be appropriate for seabird bycatch assessment when spatial variation is not a concern; the SEM could be an alternative when observed data vary greatly over space.
The spatial management of fisheries has been repeatedly proposed as a discard mitigation measure. A number of studies have assessed the fishing suitability of an area based on units of by-catch or discard per unit effort. However, correct identification of fishing-suitable areas should assess biomass loss with respect to the benefits. This study therefore, proposes the analysis of by-catch ratios, which do represent benefit vs. loss and are standardized to a wide range of effort characteristics. Furthermore, our study proposes the use of two ratios: the proportion of total unwanted biomass out of the total catch as an indicator of the overall ecological impact, and the proportion of unwanted but regulated species biomass as a proxy for the economic impact on fishers resulting from the new European discard ban that prohibits the discard of regulated species. These discard ratios are modelled by means of a Bayesian hierarchical model, specifically, a spatio-temporal beta regression model, which has several advantages over the traditional arcsine transformation. Results confirm the standardizing capacity of by-catch ratios across vessels and identify at least two economically fishing-suitable areas where discards ratios are minimized by reducing unwanted catch.
The composition and structure of discard, as well as the damage caused to target and non-target species, was analyzed in 95 commercial fishing hauls carried out between March 2013 and March 2014 by the mechanized dredging fleet targeting wedge clam (Donax trunculus) in the northern Alboran Sea (southern Spain). A large proportion of the catch (ca. 42% weight) is discarded, mainly wedge clam undersized individuals and non-commercial molluscs, decapods and echinoderms. Total discards within the study period showed a high species richness, with a total of 84 taxa discarded, and biomasses ranging from 337.1 to 8532.5 g haul−1 (1579.9 ± 157.9 g haul−1, mean ± SE), with maxima in spring. The composition, structure and biomass of discards displayed significant differences among study sites due to differences in the benthic communities of the fishing grounds. Individuals displaying intermediate (intermediate survival chance) and severe (low survival chance) damage in the discard displayed higher values when gravel and bioclastic material was more abundant in the catch. Overall, 15% of the discarded individuals displayed any type of damage, from which 12% were severely damaged, and with Echinoderms displaying the highest mean proportion of damaged individuals (79.5 ± 2.9% of individuals). The target species displayed a high proportion of undamaged individuals to fishing impacts, which may represent an important factor for the maintenance of populations of this commercial species on the fishing grounds.
As fisheries shift towards ecosystem-based management, the need to reduce impacts on by-catch has been increasingly recognised. In this study the catch composition, discard rate, and post-capture survival of species caught by gillnets in Tasmania, Australia, was investigated. Over half the commercial gillnet catch was discarded, with discard rates of ~20% for target and >80% for non-target species. Capture condition, including initial mortality, was assessed using simple criteria for a range of species and related to soak duration. Delayed mortality was also assessed using tank trials and related to capture condition. By combining initial and delayed mortality rates post-capture survival was estimated. Longer soak durations generally resulted in slight, but significant, declines in capture condition and lower initial survival. Nonetheless, when combined with delayed survival, four of the five most commonly caught species (Cheilodactylus spectabilis, Latridopsis forsteri, Aplodactylus arctidens, Cephaloscyllium laticeps) exhibited high post-capture survival (83–100%) for soak durations within the maximum regulated range. Post-capture survival of the one remaining commonly caught species, Notolabrus tetricus, (typically discarded) declined with increased soak duration from 84% to 62%, suggesting that this species would benefit from a further reduction in maximum soak duration. Initial and delayed survival rates for the species retained for tank trials exhibited a significant linear relationship, which was used to estimate delayed survival rates for the rarer species. This method enabled the estimation of potential post-capture survival rates for a diverse range of species and may have application in other data-limited situations where the relationships between fishing practices and by-catch survival are uncertain. Overall, our results suggest that soak duration regulation has been effective in reducing by-catch mortality for many species, noting that some species have low survival rates regardless of soak duration.
Common dolphins (Delphinus delphis) are responsible for the large majority of interactions with the pole-and-line tuna fishery in the Azores but the underlying drivers remain poorly understood. In this study we investigate the influence of various environmental and fisheries-related factors in promoting the interaction of common dolphins with this fishery and estimate the resultant catch losses. We analysed 15 years of fishery and cetacean interaction data (1998–2012) collected by observers placed aboard tuna fishing vessels. Dolphins interacted in less than 3% of the fishing events observed during the study period. The probability of dolphin interaction varied significantly between years with no evident trend over time. Generalized additive modeling results suggest that fishing duration, sea surface temperature and prey abundance in the region were the most important factors explaining common dolphin interaction. Dolphin interaction had no impact on the catches of albacore, skipjack and yellowfin tuna but resulted in significantly lower catches of bigeye tuna, with a predicted median annual loss of 13.5% in the number of fish captured. However, impact on bigeye catches varied considerably both by year and fishing area. Our work shows that rates of common dolphin interaction with the pole-and-line tuna fishery in the Azores are low and showed no signs of increase over the study period. Although overall economic impact was low, the interaction may lead to significant losses in some years. These findings emphasize the need for continued monitoring and for further research into the consequences and economic viability of potential mitigation measures.