2004 IUCN red list of threatened species : a global species assessment

The depletion of fish stocks from global fisheries has been a long-standing concern. More recently, incidental catch of non-target (termed bycatch) vertebrates also has been proposed as a serious conservation issue. Here we present a bycatch assessment for loggerhead and leatherback sea turtles that are incidentally caught by global pelagic longlines. We integrate catch data from over 40 nations and bycatch data from 13 international observer programmes. Despite infrequent rates of encounter, our analyses show that more than 200 000 loggerheads and 50 000 leatherbacks were likely taken as pelagic longline bycatch in 2000. Our analyses suggest that thousands of these turtles die each year from longline gear in the Pacific Ocean alone. Given 80‐95% declines for Pacific loggerhead and leatherback populations over the last 20 years, this bycatch level is not sustainable. Adopting a large-scale, synthetic approach is critical to accurately characterize the influence of global fisheries bycatch on globally distributed and imperilled pelagic vertebrates.

/pdf/quantifying-the-effects-of-fisheries-on-threatened-species-uqrk6q16kv.pdf

Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on loggerhead and leatherback sea turtles

Despite being one of the most common pieces of information used in assessing the status of fish stocks, relative abundance indices based on catch per unit effort (cpue) data are notoriously problematic. Raw cpue is seldom proportional to abundance over a whole exploitation history and an entire geographic range, because numerous factors affect catch rates. One of the most commonly applied fisheries analyses is standardization of cpue data to remove the effect of factors that bias cpue as an index of abundance. Even if cpue is standardized appropriately, the resulting index of relative abundance, in isolation, provides limited information for management advice or about the effect of fishing. In addition, cpue data generally cannot provide information needed to assess and manage communities or ecosystems. We discuss some of the problems associated with the use of cpue data and some methods to assess and provide management advice about fish populations that can help overcome these problems, including integrated stock assessment models, management strategy evaluation, and adaptive management. We also discuss the inappropriateness of using cpue data to evaluate the status of communities. We use tuna stocks in the Pacific Ocean as examples.

Interpreting catch per unit effort data to assess the status of individual stocks and communities

The great mass extinctions of the fossil record were a major creative force that provided entirely new kinds of opportunities for the subsequent explosive evolution and diversification of surviving clades. Today, the synergistic effects of human impacts are laying the groundwork for a comparably great Anthropocene mass extinction in the oceans with unknown ecological and evolutionary consequences. Synergistic effects of habitat destruction, overfishing, introduced species, warming, acidification, toxins, and massive runoff of nutrients are transforming once complex ecosystems like coral reefs and kelp forests into monotonous level bottoms, transforming clear and productive coastal seas into anoxic dead zones, and transforming complex food webs topped by big animals into simplified, microbially dominated ecosystems with boom and bust cycles of toxic dinoflagellate blooms, jellyfish, and disease. Rates of change are increasingly fast and nonlinear with sudden phase shifts to novel alternative community states. We can only guess at the kinds of organisms that will benefit from this mayhem that is radically altering the selective seascape far beyond the consequences of fishing or warming alone. The prospects are especially bleak for animals and plants compared with metabolically flexible microbes and algae. Halting and ultimately reversing these trends will require rapid and fundamental changes in fisheries, agricultural practice, and the emissions of greenhouse gases on a global scale.

https://www.pnas.org/content/pnas/105/Supplement_1/11458.full.pdf

Ecological extinction and evolution in the brave new ocean

The rapid destruction of the planet's biodiversity has prompted the nations of the world to set a target of achieving a significant reduction in the rate of loss of biodiversity by 2010. However, we do not yet have an adequate way of monitoring progress towards achieving this target. Here we present a method for producing indices based on the IUCN Red List to chart the overall threat status (projected relative extinction risk) of all the world's bird species from 1988 to 2004. Red List Indices (RLIs) are based on the number of species in each Red List category, and on the number changing categories between assessments as a result of genuine improvement or deterioration in status. The RLI for all bird species shows that their overall threat status has continued to deteriorate since 1988. Disaggregated indices show that deteriorations have occurred worldwide and in all major ecosystems, but with particularly steep declines in the indices for Indo-Malayan birds (driven by intensifying deforestation of the Sundaic lowlands) and for albatrosses and petrels (driven by incidental mortality in commercial longline fisheries). RLIs complement indicators based on species population trends and habitat extent for quantifying global trends in the status of biodiversity. Their main weaknesses are that the resolution of status changes is fairly coarse and that delays may occur before some status changes are detected. Their greatest strength is that they are based on information from nearly all species in a taxonomic group worldwide, rather than a potentially biased subset. At present, suitable data are only available for birds, but indices for other taxonomic groups are in development, as is a sampled index based on a stratified sample from all major taxonomic groups.

/pdf/measuring-global-trends-in-the-status-of-biodiversity-red-4s8j8zwv5g.pdf

Measuring Global Trends in the Status of Biodiversity: Red List Indices for Birds

Summary
1 Several albatross species, including the wandering albatross Diomedea exulans, have shown marked declines in abundance throughout their range. These seabirds are frequently taken as by-catch in longline fisheries and this mortality has been implicated in the population declines. 2 We developed a deterministic, density-dependent, age-structured model for assessing the effects of longlining on wandering albatross populations. We used demographic data from field studies at South Georgia and the Crozet Islands, data on albatross abundance from 1960 to 1995, and reported effort data from the tuna longline fisheries south of 30° S, to model estimated by-catch levels and other population parameters in the model. 
3 The model used two alternative assumptions about patterns of at-sea distribution of wandering albatross (uniform between 30° S–60° S; proportional to the distribution of longline fishing effort between these latitudes).
4 Our model was able to predict reasonably closely the observed data from the Crozet Islands wandering albatross population, but the fit to the South Georgia population was substantially poorer. This probably reflects: (i) greater overlap in the Indian Ocean than in the Atlantic Ocean between the main areas of tuna longline fishing and the foraging ranges of wandering albatrosses from the Crozet Islands and South Georgia, respectively; and (ii) greater impact of poorly documented longline fisheries, especially the tuna fisheries in the south Atlantic and the Patagonian toothfish Dissostichus eleginoides fishery, within the foraging range of wandering albatrosses from South Georgia.
5 The model results suggest that the marked decline in both populations, and subsequent recovery of the Crozet Islands population (but not the continued decline of the South Georgia population), can be explained by the tuna longline by-catch. They further indicate that populations may be able to sustain some level of incidental take. However, the likely under-reporting of fishing effort (especially in non-tuna longline fisheries) and the delicate balance between a sustainable and unsustainable level of by-catch for these long-lived populations suggest great caution in any application of such findings.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.0021-8901.2001.00661.x

Modelling the impact of fishery by-catches on albatross populations

Spatio-temporal trends of longline fishing effort in the Southern Ocean and implications for seabird bycatch

http://imina.soest.hawaii.edu/PFRP/large_pelagics/polacheck_marine_policy06.pdf

Tuna longline catch rates in the Indian Ocean: Did industrial fishing result in a 90% rapid decline in the abundance of large predatory species?

We describe a novel maximum likelihood method for fitting general growth curves to tagrecapture data. The growth model allows for the asymptotic length and the time to tagging to vary from individ...

A flexible maximum likelihood approach for fitting growth curves to tagrecapture data

Summary: Most seabirds caught and killed by longline fishing are captured during line setting. Data collected by Australian observers on Japanese longline vessels from April 1992 to March 1995 were used to investigate the influence of various environmental factors and mitigation measures on seabird catch rates. Generalised linear models were used to test the significance of the effect of each factor. The environmental factor that most influenced the seabird catch rate was whether line setting was carried out at night or during the day. From the data examined, the chance of catching seabirds during day sets was five times greater than for night sets. For night sets, the chance of catching seabirds during the full half-phase of the moon was five times greater than during the new half-phase. The area and season fished were also significant, while wind, cloud and sea conditions were not. Considerable variation in the seabird by-catch rate among vessels was found. This was probably due to differences in their implementation of mitigation measures, as well as the clumped distribution of seabirds by area and time. Although the by-catch rate was significantly different among years, the differences were small in comparison to other factors. An examination of the influence of mitigation measures for sets made during the day in summer in the Tasmanian area showed that the level of bait thawing and unidentified factors related to individual vessels were most significant in determining the seabird by-catch rate, followed by the use of a bait throwing device. For this data set, the amount of cloud cover had an influence, while moon phase, sea conditions and wind strength did not. The effect of using bird scaring tori poles and lines was not examined, as these were used during all sets examined in detail.

The Influence of Environmental Factors and Mitigation Measures on By-Catch Rates of Seabirds by Japanese Longline Fishing Vessels in the Australian Region

Tom Polacheck

Papers

Modelling the impact of fishery by-catches on albatross populations

Spatio-temporal trends of longline fishing effort in the Southern Ocean and implications for seabird bycatch

Tuna longline catch rates in the Indian Ocean: Did industrial fishing result in a 90% rapid decline in the abundance of large predatory species?

A flexible maximum likelihood approach for fitting growth curves to tagrecapture data

The Influence of Environmental Factors and Mitigation Measures on By-Catch Rates of Seabirds by Japanese Longline Fishing Vessels in the Australian Region