Spiny dogfish

Background:

Currently, spiny dogfish is quite possibly the most hated organism in the world’s ocean due to its widespread reputation as a destructive “mini” eating machine. While they are one of the most abundant sharks in the ocean, they do not attract the same mesmerizing attention as their charismatic relatives. Within the Northwest Atlantic, spiny dogfish have been blamed for preventing the recovery of commercially important species including cod and haddock. Since 1963, the Northeast Fisheries Science Center (NEFSC) branch of the National Marine Fisheries Service has conducted bottom trawls to monitor trends in abundance of fishes in the Northwest Atlantic. Fluctuations in spiny dogfish abundance during these trawl surveys are thought to be a result of the variation in migration of mature and juvenile dogfish and not necessarily related to coastal population increases. They often show up in local areas in very high abundances for several months at a time. The unpredictable behavior of spiny dogfish can prove challenging to decipher between population fluxes and seasonal movements.

My research examines the long-term spatial distribution of spiny dogfish in relation to environmental conditions at time of capture. As a NOAA Sea Grant fellow, I am working with scientists from the NEFSC in Woods Hole and analyzing their bottom trawl data to help elucidate the underlying mechanisms that may explain the highly migratory behavior of spiny dogfish. In addition, I am investigating the long-term spatial relationship between spiny dogfish and important prey species over the past 46 years in the northwest Atlantic. My field work consists of working aboard the Henry B. Bigelow for a few weeks each year to gain insight into how the bottom trawl data is collected in the Northwest Atlantic. Overall, we hope this analysis will allow fishery managers to get a handle on survey variability and help in trend monitoring for spiny dogfish.

Recent papers:

Application of generalized additive models to examine ontogenetic and seasonal distributions of spiny dogfish (Squalus acanthias) in the Northeast (US) shelf large marine ecosystem. Canadian Journal of Fisheries and Aquatic Sciences.

Sagarese, S.R., M.G. Frisk, R.M. Cerrato, K.A. Sosebee, J.A. Musick, and P.J. Rago (2014).

Abstract: Increased commercial importance of spiny dogfish (Squalus acanthias) combined with an often debated, and controversial, ecological impact has warranted an investigation of the relationship among distribution, environment, and prey to better understand the species ecology and inform management. To elucidate mechanisms behind distributional changes, we modeled seasonal occurrence and abundance of neonate, immature, and mature spiny dogfish as functions of abiotic and biotic factors using generalized additive models and Northeast Fisheries Science Center bottom trawl survey data. Significant nonlinear relationships were widespread throughout dogfish stages and seasons. Seasonal occurrence was tightly linked to depth and bottom temperature, with year and Julian day influential for some stages. While these factors also influenced abundance, ecological factors (e.g., squid abundances) significantly contributed to trends for many stages. Potential impacts of climate change were evaluated by forecasting distributions under different temperature scenarios, which revealed higher regional probabilities of occurrence for most stages during a warmer than average year. Our results can be used to better understand the relationship between sampling periods and movement drivers to survey catchability of the population in the Northeast (US) shelf large marine ecosystem.

Paper highlights:

Fig. 9. Hypothetical predicted probability of (a) mature female and (b) neonate spiny dogfish occurrence during spring in the Northeast (US) shelf large marine ecosystem for a year exhibiting average (BTavg), warmer (BTavg + 1 °C), and cooler (BTavg – 1 °C) bottom temperatures. MA, Mid-Atlantic Bight; SNE, Southern New England; GB, Georges Bank; and GM, Gulf of Maine. Note that only the abiotic submodel was used for prediction because of uncertainty regarding how prey species would respond to temperature changes. (For the coloured version of this figure, refer to the Web site at http://www.nrcresearchpress.com/doi/full/10.1139/cjfas-2013-0342.)

Figure 9

Influence of environmental, spatial, and ontogenetic variables on habitat selection and management of spiny dogfish in the Northeast (US) shelf large marine ecosystem. Canadian Journal of Fisheries and Aquatic Sciences, 71: 567–580.

Sagarese, S.R., M.G. Frisk, T.J. Miller, K.A. Sosebee, J.A. Musick, and P.J. Rago (2014).

Abstract: Declines in abundance of commercially valuable groundfish have highlighted the ecological and commercial importance of previously underutilized elasmobranchs in the Northeast (US) shelf large marine ecosystem (NES LME). Seasonal distributions and ontogenetic habitats of one such species, spiny dogfish (Squalus acanthias), were investigated using Northeast Fisheries Science Center (NEFSC) bottom trawl survey data (1963-2009). Neonate, immature, and mature dogfish all selected warmer, more saline, and more southerly locations during spring compared with available locations. During autumn, larger dogfish occupied relatively warmer, shallower, and less saline waters while neonates selected higher salinities. There were strong ontogenetic patterns in habitats occupied. Contrary to expectation, geographic range contracted as abundance increased during autumn. This suggests that niche constraints override density-dependent effects, although detection of relationships within stages was limited by low statistical power. The proportion of mature female survey catch within the Mid-Atlantic Bight was significantly related to temperature, suggesting that environmental conditions surveyed may impact population trends. Collectively, these results highlight critical habitats, suggest mechanisms behind ontogenetic habitat selection, and provide insight into how changing environmental conditions may impact stock assessment.