| dc.description.abstract | Human activities have a major effect on the world’s ecosystems including the marine
environment, where harvesting practices often target individuals based on specific traits,
resulting in selective fishing. This selective pressure has the potential to induce changes in the
behavioural, morphological, physiological, and genetic composition of marine populations.
Understanding the selectivity is important for understanding the consequences of different
fisheries. The declining Norwegian catches of European lobster have led to the
implementation of lobster reserves all along the Norwegian southern and western coast. These
no-take zones have given researchers the opportunity to study lobster populations in the
absence of selective fishing. As a part of a monitoring program, an annual trap survey has
been conducted in Flødevigen lobster reserve since 2004. However, the much higher density
of lobsters in the reserve area has raised concerns about the catchability and its effect on
monitoring results. In this thesis, catch data from one year of the annual lobster survey is
compared to a stand-alone fishing survey using a higher trap density and restraint of lobsters.
This comparison aims to see how fishing with a different method influences the catches.
Additionally, a behavioural experiment in the laboratory investigates the relationship between
crusher claw size and behaviour in male lobsters. As males grow larger claws inside the
reserve, it has been hypothesized that males with large claws have a higher catchability
because of their behaviour. Results indicate that fishing with a higher trap density and
restraint of lobsters leads to reduced catch per unit effort (CPUE,) decreased mean total
length, a higher proportion of berried females and larger relative claws for both males and
females. However, the behavioural experiment revealed no effect of claw size on behaviour.
Behaviours tested were time spent in shelter, number of times entering shelter, activity,
position in tank and reaction to a food box. Nonetheless, there was a notable individual
behaviour among lobsters, by significant repeatability for lobster ID for all behaviours tested.
These findings suggest that fishing with different methods can result in catches with different
demographic compositions from the same population. Furthermore, lobsters show consistent
individual behaviour in relation to shelter usage, activity, position in the tank, and reaction to
food, which likely influence their attraction to baited traps and ultimately the catchability. | |
