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The world tuna fishing fleet is dominated by purse seine boats. Purse seine sets are sometimes unsuccessful in capturing fish; these unsuccessful attempts are known as null sets. Null sets have been widely documented and the numbers indicate that they happen in large proportions. In Mexico, the tuna fishery represents the second most important fishery by volume and value. The frequency of occurrence of null sets during the period 2000-2013 was analyzed to identify the regions, periods, and oceanographic conditions (e.g., ENSO) related to them. Null sets on free-swimming fish schools and between June and July had a higher relative representation. The region with highest relative occurrence was the mouth of the Gulf of California (between August and October). A positive correlation was observed between the occurrence of null sets on free-swimming fish schools and the Multivariate El Niño Index. The maximum values of occurrence of null sets were related to those months in which the water column structure presented changes. Comprehension of this phenomenon (null sets) and its relation to natural events is of importance for the fishery, as there could be repercussions for the economy and management of the resource. [ABSTRACT FROM AUTHOR]

Wahoo (Acanthocybium solandri) is distributed in all tropical and subtropical oceans and caught incidentally by the tuna purse-seine fishery in the Eastern Pacific Ocean (EPO). Generalized additive models (GAM) and boosted regression trees (BRT) were used to analyze relationships between presence of wahoo in logbook data from the Mexican tuna purse-seine fishery with environment, geographic area and set type (unassociated, associated with dolphins or floating objects set). Model performance was evaluated using changes in deviance in the fitted models and the area under the receiver operating characteristic curve (ROC). Results indicate little difference between the performance of GAM and BRT models. Both methods were consistent with predictions of presence of wahoo with respect to the variables used. Set type was the single most important predictor of variation in presence of wahoo, with highest probability of incidental catch in sets made on floating objects. With respect to environmental factors, sea surface temperature (20–25°C) and chlorophyll-a concentration (<2mgm−3) determined the highest probability of incidental catch of wahoo. The coast of Baja California Sur, Mexico and south of the equator were predicted to have a high probability of incidental catch of wahoo. [Copyright &y& Elsevier]

Abstract: In the eastern Pacific Ocean (EPO), dolphinfish (Coryphaena spp.) are caught incidentally by the tuna purse-seine fishery; therefore, the records of this fishery are a good source of information to analyze the distribution of dolphinfish. To determine the spatiotemporal distribution of dolphinfish and catch variability in the three types of tuna-fishing sets (on schools associated with dolphins or with floating objects, or on unassociated schools), statistical analyses were made of the 1998–2005 records taken by scientific observers on board tuna-fishing vessels. The incidental catch did not show a well-defined annual or seasonal distribution pattern. Two high catch areas were observed, the first located in Mexican offshore waters (15–25°N), with 15% of the total catch, and the second located in offshore waters of the central EPO (0–10°N), with almost 60% of the total catch. The incidental catch was significantly different among years and seasons (H 7,780 =54.6, p <0.05 for years, and H 3,780 =42.7, p <0.05 for seasons), the greatest catch being recorded during 1999 and the first two quarters, respectively. Sets on floating objects recorded most of the incidental catch of dolphinfish, followed by unassociated sets, while dolphin-associated sets recorded the lowest catch. Almost 80% of the total catch was fished in waters with sea-surface temperatures between 25°C and 28°C. The mean size of dolphinfish was significantly different (H 2,777 =12.8, p <0.05) by set type, but the smallest specimens caught were associated with floating objects. Among sets associated with floating objects, the incidental catch of dolphinfish was greatest in sets on logs, branches, etc. (PALO sets), though those on FADs (fish-aggregating devices) were the most numerous in the central EPO. [Copyright &y& Elsevier]