RISK FACTORS AFFECTING THE VAQUITA (PHOCOENA SINUS)1

Despite the vaquita being commonly cited as one of the most endangered marine mammals in the world, there is still disagreement over which factors put the species at greatest risk of extinction. This lack of agreement hinders management decisions needed to reduce the risk to the species. To expedite decision-making we consider four major risk factors. Habitat alteration from reduced flow of the Colorado River does not currently appear to be a risk factor because productivity remains high in vaquita habitat. Pollutant loads are low and pose low to no risk. Reduced fitness from inbreeding depression and loss of genetic variability are unlikely to pose high risk currently, though risk will increase if vaquitas remain at low abundance over long periods of time. Mortality resulting from fisheries bycatch poses high risk. Thus, short term management should not be hindered by uncertainty in estimating the risk of these factors, and primary conservation efforts should be directed to wards immediate elimination of incidental fishery mortality.     

Population structure of bycaught harbour porpoise (Phocoena phocoena) in Norway

ABSTRACT

The preference for coastal habitats makes the harbour porpoise, Phocoena phocoena, vulnerable to fisheries conflicts and hence prone to die due to entangling in fishing nets. An opportunistic sampling of such casualties (134 individuals) in Norwegian waters was used to assess the genetic population structure of the species by SNP-genotyping at 78 loci. The results of genetic clustering obtained for these individuals failed to identify more than one genetic group. Likewise, the individually-based F did not meet an Isolation-by-Distance pattern, thus supporting the conclusion that harbour porpoise in Norway probably belongs to a single genetic group or population.     

REDUCING INCIDENTAL MORTALITY OF FRANCISCANA DOLPHIN PONTOPORIA BLAINVILLEI WITH ACOUSTIC WARNING DEVICES ATTACHED TO FISHING NETS

We conducted a double blind experiment in an artisanal gillnet fishery in Argentina to determine the effectiveness of acoustic deterrents (pingers) at reducing bycatch of the Franciscana dolphin ( Pontoporia blainvillei ). The fishery was conducted by small inflatable and fiberglass vessels operating between 0.5 and 7 krn from the coast. Each vessel carried an independent observer who was rotated from vessel to vessel throughout the course of the experiment. Information on the number of dolphins captured, geographic position, depth, configuration of fishing gear, soak time, biomass of fish caught, and sea lion predation in a string/net producing any damage was recorded. Equivalent numbers of active and silent pingers were used during the experiment. A total of 45 dolphins were caught in the silent nets, and seven were caught in the active pinger nets, demonstrating a highly significant reduction in bycatch for this species. However, sea-lions ( Otaria flavescens ) damaged the fish in active pinger nets significantly more than silent nets, and the damage increased over the course of the experiment. Although pingers show promise as a management tool for this species, pinniped depredation suggests that higher pinger frequencies will be needed to avoid a "dinner bell" effect.     

A BAYESIAN ANALYSIS TO ESTIMATE LOSS IN SQUID CATCH DUE TO THE IMPLEMENTATION OF A SEA LION POPULATION MANAGEMENT PLAN

This study estimates the effect of a sea lion ( Phocarctos hookeri ) population management plan on both the sea lion population and the associated squid ( Nototodarus sloanii ) fishery. The goal of the management plan is to rebuild the sea lion population and involves closing the squid fishery when a threshold level of sea lions have been caught. The threshold level is calculated from a generalized simulation analysis which conservatively allows for adequate population rebuilding for a number of different species and populations. Our analysis uses Bayesian theory to describe uncertainty in the sea lion population site and squid catch under the implementation of the management plan. The priors represent this particular sea lion population, and the analysis represents expectation rather than calculating conservative levels of safe fishing-related mortality. The results show that the squid catch is very sensitive to whether or not the squid fishery is closed when it exceeds the threshold level for sea lion bycatch. The sea lion population size is much less sensitive to the closure of the squid fishery. For an economically important fishery, the estimates of uncertainty in both loss of catch and increase in sea lion population are needed to allow informed decision-making about trade-offs between sea lion conservation and full exploitation of the fishery.