Abstract
This study examined diversity and habitat characteristics for bycatch assemblages in two different types of fishing (drifting fish aggregating devices sets and sets made on school of tunas) in the eastern Pacific Ocean (20oS-30oN and 70o-150oW) between 2005 and 2011 using biodiversity metrics and Generalized Additive Models. Bycatch information was based on data collected by onboard observers covering more than 80% of the purse seine fishing trips. Our results suggest that diversity and habitat characteristics of the bycatch assemblages differ depending of the fishing mode. Thus, diversity was mostly explained by area and set type; being higher in FAD sets than School sets. Concretely, diversity seems to be directly related with the equatorial upwelling and the front system in FAD sets and with the Costa Rica Dome and the coastal upwelling of Panama induced by wind jets in School sets. Among environmental variables, temperature and chlorophyll were the most important predictors to describe the diversity of the bycatch assemblages. This work has investigated multiple indicators related to the bycatch assemblages and their habitat, which could be helpful for the development of an Ecosystem Approach to Fishery Management.
Highlights
Fishing is one of the recognized causes of marine biodiversity loss (Worm et al, 2006), especially when fishing activity alters the diversity, composition, biomass and productivity of the species inhabiting the marine ecosystem by changing and reducing their habitats (Dayton et al, 1995).Various Regional Fishery Management Organizations have implemented measures to regulate and reduce catches of overfished single species (Cullis-Suzuki and Pauly, 2010)
The Chao2 estimator showed that a total of 71 and 68 species could be observed in fish aggregating devices (FAD) and School sets, respectively, if the sample size is large enough (Table 1, Figure 2)
It is known that the number of species of the bycatch in FAD sets is higher than in School sets (Amandè et al, 2010; Torres-Irineo et al, 2014), our work suggests that the total number of bycatch species caught in the tropical tuna purse seiners is the same for both set types provided that sufficient sample size and the coverage rate is reached irrespective of the fishing mode
Summary
Fishing is one of the recognized causes of marine biodiversity loss (Worm et al, 2006), especially when fishing activity alters the diversity, composition, biomass and productivity of the species inhabiting the marine ecosystem by changing and reducing their habitats (Dayton et al, 1995). Various Regional Fishery Management Organizations have implemented measures to regulate and reduce catches of overfished single species (Cullis-Suzuki and Pauly, 2010). The implementation of the Ecosystem Approach to Fishery Management (EAFM), which. The objective of the EAFM is to reduce the mortality of the most vulnerable fished species and maintain the biodiversity in the marine ecosystem (Pikitch et al, 2004). Describing the spatial-temporal variability of species diversity can provide important information to facilitate the implementation of EAFM (Greenstreet and Rogers, 2006)
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