Abstract
Conflict arises in fisheries worldwide when piscivorous birds target fish species of commercial value. This paper presents a method for estimating size selectivity functions for piscivores and uses it to compare predation selectivities of Great Cormorants (Phalacrocorax carbo sinensis L. 1758) with that of gill-net fishing on a European perch (Perca fluviatilis L. 1758) population in the Curonian Lagoon, Lithuania. Fishers often regard cormorants as an unwanted “satellite species”, but the degree of direct competition and overlap in size-specific selectivity between fishers and cormorants is unknown. This study showed negligible overlap in selectivity between Great Cormorants and legal-sized commercial nets. The selectivity estimation method has general application potential for use in conjunction with population dynamics models to assess fish population responses to size-selective fishing from a wide range of piscivorous predators.
Highlights
Ecological interactions between cormorants, fish, and fishers are problematic globally [1,2,3,4,5,6,7]
In this paper we describe methods to directly estimate the parameters of selectivity functions using length composition data; simultaneous estimation of selectivity parameters for both fishing nets and piscivorous predators is achieved without an assumption of equality in fishing power among nets or predators
Our results show there is limited direct interaction between
Summary
Ecological interactions between cormorants, fish, and fishers are problematic globally [1,2,3,4,5,6,7] Among those studies describing the effects of increasing cormorant numbers on fish populations and fisheries in Europe [5,8] and North America [9,10,11] many suggest cormorants have a negative impact, and that is certainly a common perception of fishers [7]. [7,8,22,23,24]) Several assessed those fish age groups most affected by cormorant predation (see [25,26]) or considered seasonal differences in selectivity [27,28], and one focussed on size and species selectivity effects on fish community structure [29]
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