Catch=By-catch=Capture=Ship strike

Or the relative impact of different forms of direct non-natural mortality on population dynamics and conservation

Harbour porpoise in gillnet © Krzysztof Skóra-Hel Marine Station

The direct non-natural mortality includes catches and animals which are struck but lost by hunters. Moreover it also includes animals by-caught in fishing gears (dead or alive but injured) and those which die due to entanglement and ship strikes, as well as animals taken for captivity. In terms of population dynamics and management, there is no intrinsic difference between capture, by-catch, ship strikes and direct catch from whaling/sealing. All four permanently remove animals from the wild populations and should be estimated so they can be taken into account in population modelling.

Mortality due to by-catch and entanglement has long been recognised as having significant demographic effects on many populations of marine mammals and as a factor impairing the recovery of some marine mammal populations.

To fully understand the impact of these interactions, it is necessary to have mechanisms not only for monitoring population abundance and trends, catch reporting and struck and lost rates, but also to obtain reliable estimates of by-catch and ship strikes for species and areas where this might be an issue. 

The NAMMCO Scientfic Working Group on By-catch aims to identify all fisheries with potential by-catch of marine mammals and review and evaluate current by-catch estimates. The overall goal is to provide advice on improved data collection and the most reliable methodologies for estimating by-catch and mitigation methods. You will find meeting reports here.