Abstract
We developed a habitat suitability index (HSI) model to evaluate the variability of suitable habitat for neon flying squid (Ommastrephes bartramii) under anomalous environments in the Northwest Pacific Ocean. Commercial fisheries data from the Chinese squid-jigging vessels on the traditional fishing ground bounded by 35°-45°N and 150°-175°E from July to November during 1998-2009 were used for analyses, as well as the environmental variables including sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, sea surface height anomaly (SSHA) and sea surface salinity (SSS). Two empirical HSI models (arithmetic mean model, AMM; geometric mean model, GMM) were established according to the frequency distribution of fishing efforts. The AMM model was found to perform better than the GMM model. The AMM-based HSI model was further validated by the fishery and environmental data in 2010. The predicted HSI values in 1998 (high catch), 2008 (average catch) and 2009 (low catch) indicated that the squid habitat quality was strongly associated with the ENSO-induced variability in the oceanic conditions on the fishing ground. The La Niña events in 1998 tended to yield warm SST and favorable range of Chl-a concentration and SSHA, resulting in high-quality habitats for O. bartramii. While the fishing ground in the El Niño year of 2009 experienced anomalous cool waters and unfavorable range of Chl-a concentration and SSHA, leading to relatively low-quality squid habitats. Our findings suggest that the La Niña event in 1998 tended to result in more favorable habitats for O. bartramii in the Northwest Pacific with the gravity centers of fishing efforts falling within the defined suitable habitat and yielding high squid catch; whereas the El Niño event in 2009 yielded less favorable habitat areas with the fishing effort distribution mismatching the suitable habitat and a dramatic decline of the catch of O. bartramii. This study might provide some potentially valuable insights into exploring the relationship between the underlying squid habitat and the inter-annual environmental change.
Highlights
Ommastrephes bartramii, commonly known as neon flying squid, is the most abundant and economically important oceanic squid in the family Ommastrephidae widely distributed in subtropical and temperate waters of the world’s ocean [1,2,3]
The preferred ranges with high fishing efforts for each variable in October corresponded to sea surface temperature (SST) between 13 and 15°C, Chl-a between 0.4 and 0.5 mg/m3, sea surface height anomaly (SSHA) between -4 and -2 cm, and sea surface salinity (SSS) between 33.3 and 33.5 psu, respectively
The results derived from the arithmetic mean model (AMM) and geometric mean model (GMM) models showed that the percentage of fishing effort occupied only a small proportion within the habitat suitability index (HSI) value
Summary
Ommastrephes bartramii, commonly known as neon flying squid, is the most abundant and economically important oceanic squid in the family Ommastrephidae widely distributed in subtropical and temperate waters of the world’s ocean [1,2,3]. The western stock of winter-spring cohort of neon flying squid annually undertakes round-trip migration from subtropical waters into the subarctic domain [6,7], where the warm Kuroshio Current and the cold Oyashio Current meet, sustaining the most productive traditional fishing ground between 35°-45°N and 150°-175°E for the Chinese squid-jigging fishery (Fig 1). Annual catch of O. bartramii in China was maintained at 80000–100000 t, of which the western winter-spring cohort of neon flying squid was the main fishing target by the Chinese squid-jigging vessels [8]. Previous results indicated that the distribution of fishing ground and abundance of O. bartramii were closely related to meanderings of the Kuroshio and Oyashio Currents [11], the occurrence of El Niño and La Niña events [12], variations in the sea surface water temperature [13], vertical temperature structure [14] and chlorophyll-a (Chl-a) concentration [15] on the fishing ground. Nigmatullin et al [10] suggested that El Niño doi:10.1371/journal.pone.0122997.g001
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