Co-occurrence of bycatch and target species in the groundfish demersal trawl fishery of the U.S. west coast; with special consideration of rebuilding stocks

Abstract

Abstract-Bycatch and resultant discard mortality are issues of global concern. The groundfish demersal trawl fishery on the west coast of the United States is a multispecies fishery with significant catch of target and nontarget species. These catches are of particular concern in regard to species that have previously been declared overfished and are currently rebuilding biomass back to target levels. To understand these interactions better, we used data from the West Coast Groundfish Observer Program in a series of cluster analyses to evaluate 3 questions: 1) Are there identifiable associations between species caught in the bottom trawl fishery; 2) Do species that are undergoing population rebuilding toward target biomass levels ("rebuilding species") cluster with targeted species in a consistent way; 3) Are the relationships between rebuilding bycatch species and target species more resolved at particular spatial scales or are relationships spatially consistent across the whole data set? Two strong species clusters emergeda deepwater slope cluster and a shelf cluster-neither of which included rebuilding species. The likelihood of encountering rebuilding rockfish species is relatively low. To evaluate whether weak clustering of rebuilding rockfish was attributable to their low rate of occurrence, we specified null models of species occurrence. Results indicated that the ability to predict occurrence of rebuilding rockfish when target species were caught was low. Cluster analyses performed at a variety of spatial scales indicated that the most reliable clustering of rebuilding species was at the spatial scale of individual fishing ports. This finding underscores the value of spatially resolved data for fishery management.

Comparing the Performance of Four Very Large Marine Protected Areas with Different Levels of Protection

“…This overall decline of catch is not due to a decline in fishing effort or to the establishment of marine reserves. Rather, it is due to excessive fishing pressure on fish populations globally [97], notwithstanding stock rebuilding in the EEZ of a few countries that are enlightened in this regard, notably the US and Norway [98][99][100][101][102].…”

Ghosts of the deep – Biodiversity, fisheries, and extinction risk of ghost sharks

“…Ghost sharks can contribute to a considerable proportion of unintentional catch of deepwater and coastal fisheries. For example, Rabbitfish ( Chimaera monstrosa , Chimaeridae) accounted for up to 15% of discards in deepwater trawls off Ireland (Calis et al., 2005), and the White‐spotted Chimaera ( Hydrolagus colliei , Chimaeridae) was reported in 70% of inshore tows in the groundfish fishery of the U.S. west coast between 2002 and 2009 (Heery & Cope, 2014). Ghost sharks are caught in artisanal, industrial and recreational demersal gears including longlines, trawls, trammel nets and gillnets (e.g.…”

Modelling community structure and species co-occurrence using fishery observer data

“…Many studies have examined fish species assemblages using cluster analyses with fishery-independent and -dependent data (Rogers and Pikitch, 1992;Williams and Ralston, 2002;Farmer et al, 2010;Cope and Haltuch, 2012). Heery and Cope (2014) used observer data to identify groundfish assemblages from trawls off Oregon and Washington, but encountered difficulties in identifying uncommon bycatch species on a large spatial scale using presence or absence data. Shertzer and Williams (2008) identified reef fish assemblages off the southeastern United States by analysing logbook data using hierarchical cluster analyses (HCA) aggregated by year, month, area, and depth.…”