New Zealand sea lions Phocarctos hookeri and squid trawl fisheries: bycatch problems and management options

Abstract

The New Zealand (NZ) sea lion Phocarctos hookeri is one of the world's most rare and highly localized pinnipeds. NZ sea lions only breed on New Zealand's subantarctic islands, with 86% of breeding occurring on the Auckland Islands (50°S, 166°E). In 1995, the sea surrounding the Auckland Islands out to 12 nautical miles (n miles) was declared a Marine Mammal Sanctuary, primarily to protect the breeding area of this species. Subsequently, in 2003, this area became a concurrent notake Marine Reserve. Both protection measures ban commercial trawl fishing within this area. Trawling is the predominant anthropogenic impact upon this species, both through direct (mortality as a result of bycatch) and potential indirect (resource competition) effects. However, despite this areabased protection and the fisheries management measures in the surrounding waters, the species, which numbers less than 12 000 ind., has shown a 30% decline in pup production over the last 8 yr. In this paper, I review the biology, foraging ecology and management of NZ sea lions in relation to the subantarctic arrow squid Nototodarus sloanii fishery to explore alternative management options within the framework of current legalisation in New Zealand. Management options need to afford better protection for this declining species, while still allowing profitable commercial fisheries operations for arrow squid in New Zealand waters.

Investigating foraging utilization distribution of female New Zealand sea lions, Auckland Islands

“…Figure 4 shows the area utilization of female NZ sea lion weighed by colony size and squid fisheries effort kernels calculated from trawl start/stop locations from 2001 to 2007. Although the number of trawls undertaken by the fishery varies between years, there is little variation in the areas fished Chilvers 2008a). Seventy per cent of all sea lion bycatch mortality occurs within the 50% KR of fishery effort Island females tracked forage in this area, and 72% of all fishery bycatch captures of sea lions are reported in this area .…”

“…However, within this time, the species' pup production has dropped by 50%, suggesting that this management is not providing sufficient protection for this threatened marine mammal. An alternative management option would be to identify and then to implement a marine protected area within the essential foraging areas of breeding NZ sea lions that excludes the trawl fishery, but allows squid jigging, which has been shown to result in minimal pinniped bycatch; (Arnould et al 2003;Chilvers 2008a). Therefore, a better understanding of where NZ sea lions forage and their vulnerability to fisheries activities is essential.…”

“…Over the past decade, the interaction between NZ sea lions and the arrow squid (Nototodarus sloanii) trawl fishery, which operates on the Auckland Island shelf between February and May each year, has been investigated (Baird 1996;Gales and Mattlin 1997;Uozumi 1998;Costa and Gales 2000;Wilkinson et al 2003;Chilvers et al , 2006Chilvers 2008a). Squid constitute a seasonally, temporally and individually variable proportion of a sea lion's diet (Childerhouse et al 2001;Meynier et al 2009).…”

“…Squid constitute a seasonally, temporally and individually variable proportion of a sea lion's diet (Childerhouse et al 2001;Meynier et al 2009). However, because some sea lions forage on and trawlers target the same prey near the main breeding site, up to 140 or greater than 1% of the entire estimated population of sea lions are estimated to be captured and killed in squid trawl nets during each breeding season (Baird 1996;Wilkinson et al 2003;Campbell et al 2006;Chilvers 2008a).…”

“…This is referred to as the Fishery-Related Mortality Limit (FRML). A FRML has been utilized for the last 12 years with fisheries being officially closed five times, attempted to be closed but overturned by court cases three times and had the fishing industry voluntarily withdrawal twice (Chilvers 2008a). However, within this time, the species' pup production has dropped by 50%, suggesting that this management is not providing sufficient protection for this threatened marine mammal.…”