Acoustic monitoring of lobster (Homarus gammarus) behavior and survival during fishery

Abstract

Overfishing is considered as the most important threat to many harvested marine species. This is also the case for the European lobster (Homarus gammarus). The still heavily harvested Norwegian population has been exploited to a barely sustainable level. The main aim of this study was to use automated acoustic tracking to investigate lobster behavior and survival during the lobster fishery season. In August 2011, 50 male lobsters above minimum legal size (MLS) were tagged with acoustic transmitters in an area near Arendal on the Norwegian Skagerrak coast. The data gathered were used to investigate movement variables and their effects on survival of individuals. Eight lobsters were censored from further analysis due to molting/loss of signal. Out of the 42 lobsters monitored at the onset of the fishing season, 35 were confirmed harvested and only seven survived the fishery. Other main findings suggested that lobsters avoiding trap dense areas survived (p = 0.046). Also, the observed mortality rate of 83.3% (± 5.75% SE) suggests that fishing depletes the catchable lobster population at an alarmingly high rate. This puts a strong harvest selection in favor of individuals being smaller than MLS (i.e., selection for slow growth) and movement behaviors avoiding areas considered as typical lobster habitat by fishers.