Variation in yellowfin tuna (Thunnus albacares) catches related to El Niño-Southern Oscillation events at the entrance to the Gulf of California

Fishery catch data on yellowfin tuna (Thunnus albacares) were examined to study the effects of El Niño events between 1990 and 1999 for an area in the northeastern tropical Pacific (18−24°N, 112−104°W). The data were extracted from a database of logbook records from the Mexican tuna purse-seine f leet. Latitudinal distribution of the catches increased from south to north for the 10-year period. Highest catches and effort were concentrated between 22°N and 23°N. This area accumulated 48% of the total catch over the 10year period. It was strongly correlated with El Niño-Southern Oscillation (ENSO) events. At least two periods of exceptionally high catches occurred following El Niño events in 1991 and 1997. Peaks of catches were triggered by the arrival of positive anomalies of sea surface temperature (SST) to the area. A delay of two to four months was observed between the occurrence of maximum SST anomalies at the equator and peaks of catch. Prior to these two events, negative SST anomalies were the dominant feature in the study area and catch was extremely low. This trend of negative SST anomalies with low catches followed by positive SST anomalies and high catches may be attributed to northward yellowfin tuna migration patterns driven by El Niño forcing, a result that contrasts with the known behavior of decreasing relative abundance of these tuna after El Niño events in the eastern Pacific. However, this decrease in relative abundance may be the result of a local or subregional effect

The occurrence of yellowfin tuna (Thunnus albacares) at Espiritu Santo Seamount in the Gulf of Mexico) at Espiritu Santo Seamount in the Gulf of Mexico

Pelagic fishes are not evenly dispersed in the oceans, but aggregate at distinct locations in this vast and open environment. Nomadic species such as mackerels, tunas, and sharks form assemblages at seamounts (Klimley and Butler, 1988; Fontenau, 1991). Fishermen have recognized this behavior and have placed moorings with surface buoys in deep waters to provide artificial landmarks, around which fish concentrate and are more easily captured. These fish aggregating devices (termed FADs) are common in the tropical oceans (see review, Holland, 1996). In a sense, it may only be the larger size that separates a seamount from a man-made FAD

Seasonal changes in fish assemblage structure at a shallow seamount in the Gulf of California

Seamounts have generally been identified as locations that can promote elevated productivity, biomass and predator biodiversity. These properties attract seamount-associated fisheries where elevated harvests can be obtained relative to surrounding areas. There exists large variation in the geological and oceanographic environment among the thousands of locations that fall within the broad definition of seamount. Global seamount surveys have revealed that not all seamounts are hotspots of biodiversity, and there remains a strong need to understand the mechanisms that underlie variation in species richness observed. We examined the process of fish species assembly at El Bajo Espiritu Santo (EBES) seamount in the Gulf of California over a five-year study period. To effectively quantify the relative abundance of fast-moving and schooling fishes in a ‘blue water’ habitat, we developed a simplified underwater visual census (UVC) methodology and analysis framework suitable for this setting and applicable to future studies in similar environments. We found correlations between seasonally changing community structure and variability in oceanographic conditions. Individual species responses to thermal habitat at EBES revealed three distinct assemblages, a ‘fall assemblage’ tracking warmer overall temperature, a ‘spring assemblage’ correlated with cooler temperature, and a ‘year-round assemblage’ with no significant response to temperature. Species richness was greatest in spring, when cool and warm water masses stratified the water column and a greater number of species from all three assemblages co-occurred. We discuss our findings in the context of potential mechanisms that could account for predator biodiversity at shallow seamounts

Batch Fecundity and Spawning Frequency of Sailfish (Istiophorus platypterus) off the Pacific Coast of Mexico

To estimate batch fecundity and spawning frequency of the sailfish, Istiophorus platypterus Shaw & Nodder, off the Pacific coast of Mexico, gonads from fish sampled at five tourist ports from 1989 to 1991 were histologically analyzed. Mean batch fecundity, estimated by the gravimetric method, for 21 females was 1,710,000 ± 600,000 eggs per spawning. The relationship between batch fecundity in thousands (F) and total weight of the fish in kilograms (w) was F = -245 + 61.68 w. Of 93 mature females, 28% with hydrated oocytes indicated that the average interval between spawnings was 3.6 days

Incidental catch of the rare shortbill spearfish (Tetrapturus angustirostris) by the tuna purse seine fleet in the eastern tropical Pacific Ocean

The shortbill spearfish (Tetrapturus angustirostris) is a rare, large pelagic fish that inhabits the tropical and temperate waters of the Pacific and Indian Oceans, and it is seldom incidentally captured by the purse seine and longline tuna fleets. It is listed on the International Union for the Conservation of Nature red list as data deficient, with the population likely decreasing. The main objective of this paper is to contribute basic knowledge of the species catch rate, spatial distribution, temporal trends, and association with different types of fishing sets. A 23-year (1993–2015) database of incidental catches was analyzed; data was gathered by the observers from the Inter-American Tropical Tuna Commission aboard vessels from the international tuna purse seine fleet in the eastern tropical Pacific Ocean. We also analyzed time series of sea surface temperature (SST) from different Niño regions, and 2 climatic indices, the Oceanic Niño Index (ONI) and the Pacific Decadal Oscillation (PDO). The database included information from a total of 422,970 sets; of these, ~1% resulted in a catch of 687 spearfish. Most incidental catches occurred in waters close to the equator (10ºS to 10°N), with no apparent seasonal distribution pattern. Time-series analyses showed a significant positive trend in incidental catch (~4% per year). Weak negative correlations of incidental catches with El Niño SST and ONI suggest that spearfish prefer cool waters in zones near the Equator. The PDO seemed to be more important to spearfish than El Niño events, and it is likely playing an important role in the positive trend of incidental catches. Most spearfish catches were associated with sets made on floating objects, mainly south of the equator and west of 100ºW, highlighting the oceanic behavior of this species

Seasonal changes in fish assemblage structure at a shallow seamount in the Gulf of California

Seamounts have generally been identified as locations that can promote elevated productivity, biomass and predator biodiversity. These properties attract seamount-associated fisheries where elevated harvests can be obtained relative to surrounding areas. There exists large variation in the geological and oceanographic environment among the thousands of locations that fall within the broad definition of seamount. Global seamount surveys have revealed that not all seamounts are hotspots of biodiversity, and there remains a strong need to understand the mechanisms that underlie variation in species richness observed. We examined the process of fish species assembly at El Bajo Espiritu Santo (EBES) seamount in the Gulf of California over a five-year study period. To effectively quantify the relative abundance of fast-moving and schooling fishes in a ‘blue water’ habitat, we developed a simplified underwater visual census (UVC) methodology and analysis framework suitable for this setting and applicable to future studies in similar environments. We found correlations between seasonally changing community structure and variability in oceanographic conditions. Individual species responses to thermal habitat at EBES revealed three distinct assemblages, a ‘fall assemblage’ tracking warmer overall temperature, a ‘spring assemblage’ correlated with cooler temperature, and a ‘year-round assemblage’ with no significant response to temperature. Species richness was greatest in spring, when cool and warm water masses stratified the water column and a greater number of species from all three assemblages co-occurred. We discuss our findings in the context of potential mechanisms that could account for predator biodiversity at shallow seamounts

Mesoscale dynamics and yellowfin tuna catches in the Mexican Pacific

Catch data of the yellowfin tuna (YFT) fishery were used to study the relationship between the seasonal and spatial variations of YFT with or without the presence of mesoscale structures at the entrance to the Gulf of California (19º–24º N, 104º–112º W). The YFT catches were distributed mainly over the continental shelf and around islands and seamounts. High concentration sets of YFT occurred throughout the year around the Marías islands and Cabo Corrientes, particularly in March and June. A warm (>28ºC) coastal jet with a width of 1.5 Rossby radius (~20.6 km) was observed off Cabo Corrientes during February and April, covering all the continental shelf off Cabo Corrientes. The jet moved at an average speed of 0.31 m s–1 and extended northwards to the Roca Corbetera seamount. The interaction with cooler water generated a frontal zone around which the YFT catches were concentrated. In contrast, during March the wind field was more favorable for the development of coastal upwelling off Cabo Corrientes. We observed an upwelling region with sea surface temperature of 18ºC and an offshore width of about a 3.7 Rossby radius of cold water that covered some 2600 km2. The YFT catches occurred in warmer water north of the upwelling zone

Seasonal changes in fish assemblage structure at a shallow seamount in the Gulf of California.

Seamounts have generally been identified as locations that can promote elevated productivity, biomass and predator biodiversity. These properties attract seamount-associated fisheries where elevated harvests can be obtained relative to surrounding areas. There exists large variation in the geological and oceanographic environment among the thousands of locations that fall within the broad definition of seamount. Global seamount surveys have revealed that not all seamounts are hotspots of biodiversity, and there remains a strong need to understand the mechanisms that underlie variation in species richness observed. We examined the process of fish species assembly at El Bajo Espiritu Santo (EBES) seamount in the Gulf of California over a five-year study period. To effectively quantify the relative abundance of fast-moving and schooling fishes in a 'blue water' habitat, we developed a simplified underwater visual census (UVC) methodology and analysis framework suitable for this setting and applicable to future studies in similar environments. We found correlations between seasonally changing community structure and variability in oceanographic conditions. Individual species responses to thermal habitat at EBES revealed three distinct assemblages, a 'fall assemblage' tracking warmer overall temperature, a 'spring assemblage' correlated with cooler temperature, and a 'year-round assemblage' with no significant response to temperature. Species richness was greatest in spring, when cool and warm water masses stratified the water column and a greater number of species from all three assemblages co-occurred. We discuss our findings in the context of potential mechanisms that could account for predator biodiversity at shallow seamounts

Horizontal and vertical movements of the common dolphinfish (Coryphaena hippurus) in La Paz Bay, Mexico

The common dolphinfish (Coryphaena hippurus) is an important resource for the sport-fishing industry in Mexico. It is captured incidentally by the eastern Pacific purse-seine tuna fishery and in coastal areas by artisanal fisheries. Although it is considered a highly migratory species, only few studies of its movements are available. In this study, the behavior of the common dolphinfish was analyzed by means of acoustic telemetry at three locations within La Paz Bay (southern Gulf of California) from summer to autumn 2013. Acoustic transmitters were attached to six individuals and they were tracked for periods of up to 48 h. Every hour, vertical profiles of temperature and bathymetry were made. To determine the effect of biotic (sex) and abiotic (water temperature and depth, thermocline depth, hour, and bathymetry) variables on the horizontal and vertical movements of tagged organisms, generalized additive mixed models were applied. The results showed a tendency of horizontal movements to the southwestern zone of the bay; two individuals crossed from the eastern to the western side. The average speed was 0.51 m s–1. The vertical movements showed that the individuals spent 80% of the time above 34 m depth, of which around 45% was spent in the upper 10 m of the water column. During daylight hours they swam in shallow waters (upper 10 m) and at night they performed deeper dives (73 m maximum depth). Biotic and abiotic variables influenced both types of movements; however, bathymetry and temperature largely explained fish movements

Seasonal changes in fish assemblage structure at a shallow seamount in the Gulf of California.

Seamounts have generally been identified as locations that can promote elevated productivity, biomass and predator biodiversity. These properties attract seamount-associated fisheries where elevated harvests can be obtained relative to surrounding areas. There exists large variation in the geological and oceanographic environment among the thousands of locations that fall within the broad definition of seamount. Global seamount surveys have revealed that not all seamounts are hotspots of biodiversity, and there remains a strong need to understand the mechanisms that underlie variation in species richness observed. We examined the process of fish species assembly at El Bajo Espiritu Santo (EBES) seamount in the Gulf of California over a five-year study period. To effectively quantify the relative abundance of fast-moving and schooling fishes in a 'blue water' habitat, we developed a simplified underwater visual census (UVC) methodology and analysis framework suitable for this setting and applicable to future studies in similar environments. We found correlations between seasonally changing community structure and variability in oceanographic conditions. Individual species responses to thermal habitat at EBES revealed three distinct assemblages, a 'fall assemblage' tracking warmer overall temperature, a 'spring assemblage' correlated with cooler temperature, and a 'year-round assemblage' with no significant response to temperature. Species richness was greatest in spring, when cool and warm water masses stratified the water column and a greater number of species from all three assemblages co-occurred. We discuss our findings in the context of potential mechanisms that could account for predator biodiversity at shallow seamounts