Fish in the Northwest Atlantic Are Going Hungry New Science From Maine’s Department of Marine Resources Helps To Explain Why.
This should be an ideal time for both New England’s fishermen and conservationists. Decades of sacrifice have caused the loss of (according to some reports) over 80 percent of fishing and fishing related jobs. This period of continuous decline has ended with the rebuilding of most of the fish stocks and the stabilization of the fisheries to sustainable catch levels. The ocean has healthy populations of marine mammals where just a couple of decades ago there were few. The plan to rebuild all fish stocks to optimum levels at the same time was considered by many to be biologically impossible but nature sure showed them…didn’t it?
Many anecdotal reports indicate that all is not well in the ocean off of New England. Reports of undersized cod, scrawny haddock, tuna with low fat content and other quality issues indicate a lack of nutrition in the fish stocks that many have attributed to a lack of forage fish like sea herring. A lack of herring and especially large herring attributed for the most part to fishing activity by the herring boats has been put forth as an underlying cause. The discovery that the herring are going hungry and have seen the same type of size and quality declines related to being under-nourished as the other fish puts these misguided claims into perspective. Over-fishing of sea herring would leave plenty of food available for the remaining herring but such is not the case.
An ecosystem as vast as the ocean is difficult to understand due to the large amount of predator prey relationships and the constantly changing conditions of those relationships and the environment itself. Understanding what is going on with some of the individual species is in many ways the best method to gain insight into what is going on with the system as a whole. The Department of Marine Resources in Maine has been studying the sea herring population for the last fifty years and have recently presented a new study that describes the decline of herring size, weight and quality over the last four decades. I was lucky to have attended this excellent presentation and was very surprised by their findings as to both the depth of the decline and the strong evidence supporting the cause of it.
The presentation was called, “Where are all of the big herring? Atlantic Herring (Clupea harengus) size at age decreases over time in the Northwest Atlantic.” It was the inspiration of James Becker a marine resource specialist two with the Department of Marine Resources in Boothbay Maine. It was also the work of Adam St. Gelais a marine resource specialist one. For the study they used data from the DMR Atlantic Herring Historical Database with it’s fifty years of data from over 1.2 million individual fish. The age, lengths, whole weights, gonad weights, spawn condition, dates, gear type, catch locations and even stomach contents are all contained in the database. A wealth of historical information that can be used to spot trends and changes in the state of the Atlantic herring.
Some highlights from the presentation were herring whole weights declining 40 to 60 percent and herring lengths declining 1 to 2 inches across all age classes. The overall condition factor (A ratio of length to weight that indicates how nourished a fish is) of all age classes of herring is in a declining trend as well. The reduction in size at age is not particular to herring and has been documented in other species in the gulf of Maine. The possibility that the fishery is selecting for smaller fish or that these trends are the result of fishing activity is ruled out by the fact that the downward trend is present in all of the age classes of fish and the mean age of fish landed remains constant over time.
The hypothesis that these declines are due to environmental factors is supported by a strong correlation between fish weight and length declines and sea surface temperature variations that are part of the Atlantic Multidecadal Oscillation, an oscillating fluctuation in sea surface temperatures with a period of about 60 years. Similar environmental fluctuations across the globe have been shown to impact fish populations and set a strong precedent for the correlations shown in this study. The mechanisms for this could be food limitations or alteration of trophic composition that have an impact on both the reproductive ability and the overall condition of the fish. The availability of plankton or the lack there of was noted but not a part of the study.
I found the explanations offered in the presentation to be extremely plausable. In the last ten years there has been a remarkable decline in the amount of feed in the ocean off of New England. On herring vessels we have excellent sounding equipment and used to drive over shoals of plankton that seemed like they would never end. Today that would be a rare thing indeed to see that much feed in the water. As a kid I remember old fishermen telling me the rise and decline of fish populations is cyclical and not under the control of managers and legislators. These claims were from observations made during life times spent at sea catching fish and not from any amount of academic study, it is interesting to learn of science that seems to indicate a cyclical pattern like they described. One thing is certain if the so called “Forage fish,” do not have enough to eat, there is going to be problems in the rest of the food chain.
I would like to thank the scientists at Maine DMR for their diligence and thorough efforts. It is through excellent work in the marine sciences like theirs that the future of our marine resources and ocean ecology are preserved.
All images and video are copyrighted works all rights reserved. The graphics and science were brought to you by the scientists at Maine Department of Marine Resources and are published here with their permission.