North Pacific Spiny Dogfish Squalus Research Articles

Body-length frequency and spatial segregation of the North Pacific spiny dogfish Squalus suckleyi in Tsugaru Strait, northern Japan

The present study elucidated the length structure and habitat segregation of North Pacific spiny dogfish (SPD) Squalus suckleyi in the Tsugaru Strait of northern Japan. Length–frequency distributions using kernel density estimation were determined for SPD captured by the bottom longline fishery landed at Minmaya from 1999 to 2011 and at Ohma from 2007 to 2011. Length–frequency distributions significantly differed between landings at the two ports; SPD at Minmaya were on average larger (65–85 cm precaudal length: PCL) than at Ohma (55–75 cm PCL). This difference is evidence of the length-based spatial segregation of the SPD. The seasonal landing pattern of the SPD was also different between the two ports. The SPD landed at Minmaya were largest during February–June and SPD < 75 cm PCL were caught at Ohma throughout the year. This different landing pattern was related to seasonal differences in bottom-layer water temperatures between the two fishing grounds. Females were thought to be dominant at Minmaya, whereas males dominated in most of the catches at Ohma. These results suggest spatial patterns of sexual segregation for this species in the Tsugaru Strait and require elucidation of the SPD stock condition at Minmaya and Ohma.

The activity of the rectal gland of the North Pacific spiny dogfish Squalus suckleyi is glucose dependent and stimulated by glucagon-like peptide-1.

Elasmobranchs possess a specialised organ, the rectal gland, which is responsible for excreting sodium chloride via the posterior intestine. Previous work has indicated that the gland may be activated by a number of hormones, some of which are likely related to the salt or volume loads associated with feeding. Furthermore, evidence exists for the gland being glucose dependent which is atypical for an elasmobranch tissue. In this study, the presence of sodium-glucose co-transporters (SGLTs) in the rectal gland and their regulation by feeding were investigated. In addition, the hypothesis of glucose dependence was examined through the use of glucose transporter (GLUT and SGLT) inhibitors, phlorizin, Indinavir, and STF-31 and their effect on secretion by the rectal gland. Finally, the effects on rectal gland activity of insulin, glucagon, and glucagon-like peptide-1, hormones typically involved in glucoregulation, were examined. The results showed that sglt1 mRNA is present in the gland, and there was a significant reduction in sglt1 transcript abundance 24h post-feeding. An almost complete suppression of chloride secretion was observed when glucose uptake was inhibited, confirming the organ's glucose dependence. Finally, perfusion with dogfish GLP-1 (10nmolL-1), but not dogfish glucagon, was shown to markedly stimulate the activity of the gland, increasing chloride secretion rates above baseline by approximately 16-fold (p < 0.001). As GLP-1 is released from the intestine upon feeding, we propose that this may be the primary signal for activation of the rectal gland post-feeding.

Ecosystem-level consequences of movement: seasonal variation in the trophic impact of a top predator

Spatio-temporal patterns of species abundance influence the strength of trophic interactions, while movement of individuals helps determine those patterns of abundance. Thus, understanding movement is a basis for quantifying interactions within a food web. In Puget Sound, Washington, USA, the North Pacific spiny dogfish Squalus suckleyi is an abundant top predator with a diverse, generalist diet. Coastal dogfish populations make seasonal north-south migrations, but populations in inland waters are thought to be more resident. In this study, we combined acoustic telemetry and bioenergetics modeling to determine patterns of movement and to quantify seasonal variation in the predatory impact of dogfish in Puget Sound. All tagged dogfish migrated out of Puget Sound in the winter and were absent until the following summer. Individuals that returned to Puget Sound in subsequent years showed consistent timing and duration of residence across years, but these metrics varied across individuals. Incorporating movement data into the bioenergetics model resulted in a 70% decrease in the predatory impact of dogfish in the winter and a 30 % decrease in the summer, compared to a year-round resident Puget Sound population. Incorporating metrics of movement into food web or ecosystem models will increase our understanding of species interactions and will improve our ability to predict changes in food web dynamics under various environmental and management scenarios.

New data on the distribution and size composition of the North Pacific spiny dogfish &lt;i&gt;Squalus suckleyi&lt;/i&gt; (Girard, 1854)

The results of long-term research on the spatial and vertical distribution of the North Pacific spiny dogfish Squalus suckleyi in the North Pacific Ocean and its size composition are presented. In total, data from 7059 catches of this species were analyzed (3178 with associated capture depth). The description of size composition is based on measurements of 413 specimens caught by driftnets, 328 by pelagic trawls and 722 by bottom trawls. This species was found to be most widely distributed in the North Pacific in the summer and autumn months during feeding migrations. Seasonal and long-term changes in the spatial distribution were observed. A wide distribution of S. suckleyi in the Bering Sea was recorded after the year 2000, which is likely associated with recent climate change. Occurrence of the species in the water column and near the bottom differed considerably. In the water column, the maximum number of captures was observed within the upper 25 m layer (about 90%). Near the bottom, this species was most abundant at depths less than 50 m (over 45%) and within a depth range of 101-200 m (about 50%). The catch of S. suckleyi during the daytime was considerably larger than in the night, possibly due to vertical diurnal migrations. This species was found at water temperatures ranging from 0 to 12.7°C, and maximum catches were observed at temperatures over 8°C. Size compositions of bottom and pelagic trawl catches were similar (mean length 69.1 and 68.6 cm respectively) while driftnet catches were composed of larger specimens (mean length 75.3 cm).