On January 13, 2012, Jud Crawford, science and policy manager of the Pew Environment Group's Northeast Fisheries Program, wrote about the recent Gulf of Maine cod stock assessment. He asserts that "In terms of science, nothing went wrong in 2011," but many scientists, council members, and industry members have, in fact, pointed out serious issues with the 2011 stock assessment.
In an analysis below, Saving Seafood examined the assertions made by Dr. Crawford and looked at important, relevant issues that were omitted in his assessment.
Many in New England were recently stunned by the news that the region’s prized codfish are in much deeper trouble than anyone had realized. The bleak conclusion of the most recent scientific assessment was unexpected, because just three years earlier cod appeared to show signs of recovery. Fishermen, scientists, and others have rightfully been asking, “What happened?”
The stock assessment meetings, which typically span almost a year, are open to the public, so I was able to observe the 2008 and the 2011 peer review meetings for cod. The periodic evaluation of fish stocks in New England is rigorous, comprehensive, and transparent, and it includes independent scientific experts from around the world. Gulf of Maine cod was no exception.
The Northeast Fisheries Science Center and the assessments that take place there have been the subject of many reviews, including one ordered by Congress and carried out by the National Academy of Sciences. These evaluations never revealed major deficiencies in the science and produced recommendations that have made the science even stronger, including a first-rate system of independent peer review. Teams of qualified scientists examined data, developed models, and analyzed results of the 2008 and 2011 assessments.
The 2011 assessment was especially thorough, with every imaginable angle known to the scientists at the time considered, models run and rerun, within the constraints of the available information. With the benefit of hindsight, however, it now appears that the 2008 assessment, which was based on then-current data, produced an overly optimistic forecast. Additional data, and improvements in the analyses, show that cod were actually in much poorer condition four years ago than was believed, and the situation has not gotten better.
In terms of science, nothing went wrong in 2011. What went right was the development of stronger models based on better statistics. The new assessment draws from more extensive data, including new information on mortality due to recreational fishing and small cod discarded at sea (which usually die). Additionally, it is now clear that the cohort of young fish from 2005, and which caused much of the optimism in 2008, was not as big as previously thought. As a result, this updated information (data through 2010) led to an improved, though smaller, estimate of the overall stock size, or biomass.
Read the full article at the Pew Environment Talking Fish blog.
Analysis:
The 2008 (GARM III) and 2011 (SAW 53) Gulf of Maine cod stock assessments diverge widely and present two contrasting pictures of the health of the Gulf of Maine cod stock. The article claims that, “in terms of science, nothing went wrong in 2011.” However, several methodological problems, some of which have been present in previous assessments and some that are new for the 2011 assessment, cast doubt on whether it is more accurate than the 2008 assessment.
There is always a degree of uncertainty in measuring and assessing fish stocks, but the 2011 assessment introduces new potential sources of error, whose effect on the reliability of the results is undetermined. The Bigelow, a new research vessel tasked with collecting the data used in the 2011 assessment, features several important differences from the previous research vessel, the Albatross. Most importantly, the Bigelow is significantly larger than the Albatross; it’s big enough that it can’t navigate the shallower waters in the region that Gulf of Maine cod inhabit and both commercial and recreational cod fishermen frequent. As a result, it was unable to include in the assessment any of the abundant cod that swim in the shallower waters.
The differences between the Bigelow and the Albatross can affect the accuracy and reliability of the survey in other ways. In addition to being a larger boat, the Bigelow also uses different gear, which changes what and how much it could catch. In an attempt to normalize results between assessments, NOAA estimated that the Bigelow can catch twice as many large cod and six times as many small cod as the Albatross. NMFS used this estimate to derive the coefficients used to calibrate its assessment. However, whether or not the estimates and resulting calibrations are accurate is a reasonable point of debate, and introduces even more uncertainty into the 2011 assessment.
In addition to a change in research vessels, an anomalously high estimate of recreational catch also provides a new source of potential error in the 2011 assessment. There is a legitimate question in whether the measurement of the size of the recreational fishery is an accurate representation of recreational fishing activity. The 2011 assessment concluded that half of all 2010 recreational fishing activity occurred in just a two-week period in the spring. Further, it concluded that 60% of the recreational catch came from private day boats. Both results are unusual for the recreational fishery, and more likely reflect errors in the methodology and uncertainty in the data than they do an accurate picture of recreational fishing activity.
New sources of uncertainty in the 2011 assessment are compounded by several persistent problems in methodology that have existed in previous assessments and remain in the 2011 edition. In particular, the assessment makes several assumptions about stock identification that may not be accurate. Under current models, Atlantic cod (in U.S. waters) is assumed to be two separate stocks (Gulf of Maine and Georges Bank), with no exchange or interaction between the two. Based on data from tagging surveys, which shows at least some migration between the two areas, this is an assumption that is not likely true. Similarly, the boundaries for identifying and separating the stocks are also not likely correct, and have the potential to miss cod that travel out of range of the assessment, which may result in an inaccurate assessment of the population.
Some information that was not considered in the 2011 assessment indicates an increasing stock. For example, measurements of catch-per-unit-of-effort (CPUE) in both the recreational and commercial fisheries show an increase since the 2008 assessment, which potentially indicate an increase in available catch. A trend of increasing CPUE goes against claims of a biomass radically smaller than in 2008; while the assessment would imply that cod would become more difficult to catch, the CPUE data collected suggests that the opposite is occurring. Combined with potential sources of uncertainty introduced in the 2011 assessment, statistics such as these indicate that the most recent assessment may be much more inaccurate than the previous findings in 2008.