GFDL - Geophysical Fluid Dynamics Laboratory

Cusk (Brosme brosme) and climate change: assessing the threat to a candidate marine fish species under the U.S. Endangered Species Act

January 8th, 2013

Jonathan Hare (NOAA/NMFS), John Manderson (NOAA/NMFS), Janet Nye (EPA), Michael Alexander (NOAA/OAR/ESRL), Peter Auster (Univ. of Connecticut), Diane Borggaard (NOAA/NMFS), Antonietta Capotondi (NOAA/OAR/ESRL), Kimberly Damon-Randall (NOAA/NMFS), Eric Huepel (Univ. of Connecticut), Ivan Mateo (NOAA/NMFS), Loretta O’Brien (NOAA/NMFS), David Richardson (NOAA/NMFS), Charles Stock(NOAA/OAR/GFDL), Sara Biegel (NOAA/NMFS). Journal: ICES Journal of Marine Science. DOI:10.1093/icesjms/fss160

Summary

This collaboration, led by NOAA and EPA scientists and entraining expertise from the University of Connecticut, evaluated the potential effects of climate change on cusk (Brosme brosme) in the Northwest Atlantic. Numbers of this demersal (bottom-dwelling) fish (Fig. 1) on the Northeast Atlantic continental shelf have declined dramatically over the past several decades. This is believed to be primarily a result of fishing activities. However, changes in the distribution and abundance of a number of marine fish stocks in the Northwest Atlantic have been linked to climate variability and change, suggesting that both fishing and climate may affect the future status of cusk.

A habitat model for cusk was constructed from over forty years of fishery-dependent trawl surveys from Cape Hatteras, North Carolina to New Brunswick Canada. Cusk presence was related to bottom temperature and a terrain ruggedness index using a Generalized Additive Modeling (GAM) approach. A bottom temperature climatology was constructed from over thirty years of hydrographic data. Projected temperature changes from eight different climate models and three different emissions scenarios (B1, A1B and A2) were applied to this climatology and analyzed for the periods 2020-2060 and 2060-2100.

Projected changes in bottom temperature were ~1oC for all emissions scenarios during the 2020-2060 period. Substantial cusk habitat remained throughout the western Gulf of Maine and Scotian Shelf for all scenarios during this period (Fig. 2; top panels). For 2060-2100, changes under the B1 (low emissions scenario) were ~1.5-2oC, leading to moderate projected reductions in cusk habitat. Projected 2-3oC changes under the A1B (moderate) and A2 (high) emissions scenarios, however, exhibited stark reductions and fragmentation in cusk habitat. These results suggests that climate change may pose a significant threat to cusk on the northeast U.S. shelf on the 50-100 year time scale for emissions scenarios leading to bottom temperature increases > 1.5oC.

The study offers a first assessment of the potential impact of climate change on cusk habitat. However, the models used in this study have very coarse resolution of the continental shelf. Unresolved shelf-scale processes may influence the results described above. In addition, the cusk habitat model considers only two niche dimensions (bottom temperature and bottom complexity). Other factors such as predation and competition may also influence species ranges. The impact of habitat fragmentation on cusk ecology is also not well understood. Work to address these limitations for cusk and other species on the northwest Atlantic shelf is ongoing.

Fig. 1: Cusk (Brosme brosme). Illustration courtesy of Jeff Varanyak. Cusk are relatives of cod and hake and can grow up to 1m and weigh up over 10 kg.
Fig. 1: Cusk (Brosme brosme). Illustration courtesy of Jeff Varanyak. Cusk are relatives of cod and hake and can grow up to 1m and weigh up over 10 kg.
Fig. 2: Present area of favorable cusk habitat. Green dots indicate areas where the statistical niche model predicts a net positive effect on cusk occurrence (i.e., favorable cusk habitat.
Fig. 2: Present area of favorable cusk habitat. Green dots indicate areas where the statistical niche model predicts a net positive effect on cusk occurrence (i.e., favorable cusk habitat.
Fig. 3: Projected favorable cusk habitat in 2020-2060 under and 2060-2100 under three different climate scenarios (B1 = low emissions, A1B = moderate emissions, and A2 = high emissions).
Fig. 3: Projected favorable cusk habitat in 2020-2060 under and 2060-2100 under three different climate scenarios (B1 = low emissions, A1B = moderate emissions, and A2 = high emissions).