Using opportunistic records from a recreational fishing magazine to assess population trends of sharks

BARBINI, SANTIAGO A.; LUCIFORA, LUIS O.; FIGUEROA, DANIEL E.

CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES

NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS

Lugar: Otawa; Año: 2015 vol. 72

0706-652X

Detecting and determining changes in the occurrence and abundance of species is a priority for effective managementof resources and for conservation of biodiversity. In the absence of long-term monitoring data, potential population declinesmay be very difficult to establish. Therefore, alternative information on occurrence of species to infer population trends is highlyvalued. Records of sharks (i.e., Notorynchus cepedianus, Carcharias taurus, Galeorhinus galeus, and Carcharhinus brachyurus) off northernArgentina from a recreational fishing magazine (Weekend), between 1973 and 2008, were reviewed with the aim of evaluatingpopulation trends with opportunistic data sources. For each shark species, the number of occurrences per year in the magazinewas registered. Our analyses were based on a nonprobabilistic method (McPherson and Myers? approach) designed to determinepopulation trends with opportunistic sighting records. In this approach we included the number of classified ads offering fishingguide services published per year in the magazine as a measure of observation effort. For each species, we fitted generalizedlinear models with a Poisson error structure and a log link, where the response variable was the number of occurrences per year,the explanatory variable was the year, and the logarithm of the number of fishing guide ads was specified as an offset in eachmodel. For both approaches, the models estimated that populations of the four shark species have suffered declines. Estimatesproduced by these models will help to determine the magnitude of population changes where a paucity of data prevents moreprecise analysis.