Commentary

Are Atlantic Croakers Here to Stay?

By KENNETH W. ABLE | Jun 14, 2017
Courtesy of: Kenneth W. Able Atlantic croakers are netted off boats working out of Barnegat Light and elsewhere in South Jersey.

The Atlantic croaker is in the family of drums and croakers, so named because they can vibrate their gas bladders to create species-specific sounds. This is especially evident during the spawning season when many individuals call in choruses at the same time. These sounds have been frequently recorded by Tom Grothues, another Rutgers University fish ecologist, with an underwater recorder at Beach Haven Ridge off Little Egg Inlet in the fall of the year.

Adult croakers are easily recognized by their shape and coloration. Spawning first occurs at one year of age, but they can commonly live for 10 years. They typically spawn during late summer and fall. The larvae resemble the adults, except the tail is shaped differently and they don’t yet have adult coloration or the ability to produce sound.

Larvae can be found in the fine mesh plankton nets of the Rutgers University Marine Field Station in Little Egg Harbor Township. They are collected there from September through December as they enter estuaries at sizes of less than 1 inch. We also know from other laboratory studies that the small juveniles that have begun living on the bottom are killed by low temperatures approximating those in New Jersey during many winters. Also, mass mortalities of small juveniles have occurred in unusually cold winters in Chesapeake Bay.

We can conclude that cold winter temperatures jeopardize croaker survival as juveniles and influence how many are going to be around as adults. This response to temperature is not surprising because fish that are cold-blooded and cannot regulate their internal temperatures are greatly dependent on the external temperatures of the waters they live in.

The ease with which croakers in South Jersey are caught leads some people to believe they have always been around, but this is not the case. In the late 1920s to early 1930s they were the most abundant species in the ocean and estuaries of South Jersey. They were common in the ocean pound nets of the Crest Fishery on Long Beach Island and were commonly taken by hook and line in Barnegat Bay during the 1940s. Subsequent records of commercial fishery landings indicate they were also common in the 1950s, again in the mid- to late 1970s, and appeared again, and quite abundantly, in the 1990s. In contrast, in between those periods of abundance this southern species was not seen at all or was not very abundant. For example, in the early 1970s they did not rank in the top 20. 

The recent increase in abundance, beginning in the 1990s, corresponds to a period of warmer ocean and estuarine waters. This is consistent with the fact that 14 of the top 20 warmest years in New Jersey air temperatures over the last 122 years have occurred since 1998, according to David Robinson, the state climatologist. The greater abundance can likely be explained by the greater survival of the juveniles during the more frequent milder winters and warmer water temperatures we are experiencing in South Jersey. This winter is a prime example.

During this time of milder winters, the juveniles were more abundant in our Rutgers University Marine Field Station trawl net surveys. When they were abundant they were most common in the ocean but could be found in Great Bay and all the way up to the Mullica River. The increased survival of juveniles translates into increased abundance of adults, as in the gill net fishery out of Barnegat Light.

More detailed studies in other regions confirm that winter water temperature variability controls Atlantic croaker abundance in South Jersey. For example, the adults clearly migrate south for the winter, sometimes to below Cape Hatteras, where winter temperatures are warmer. In a detailed analysis, my colleague Jon Hare and I found that the pattern of juvenile survival with winter water temperatures and survival is true for Virginia and North Carolina as well. This conclusion is based on an analysis of water temperatures, derived from long-term records of air temperatures, from 1930 to 2002. Further, these patterns appear to be linked to the larger climate system in the North Atlantic.

Once again, the central controlling factor was not the number of larvae produced, but rather how cold the winter was and, thus, how many juveniles survived. In this example, it is clear that events during the early life history strongly influence how many croakers are going to be around to harvest as adults. The fluctuations in the abundance of croakers, at least off South Jersey, are controlled more by the environment than the fisheries for them.

However, in the last couple of years croakers have been less abundant in both the commercial and recreational fisheries in South Jersey, and that begs the question: Are they here to stay or are they going to disappear again? What does this mean for the future of croaker fishing in South Jersey? If the predictions of warmer water temperatures continue, as is happening this winter, we might expect them to be abundant in the next couple years. On the other hand, if we get multiple cold winters, especially in a row, as we did in the 1980s, there are likely to be fewer croakers around.

As importantly, are these kinds of patterns representative for other fish? We think that the recent occurrence of black drum and silver perch, other members of the croaker and drum family, in the Mullica Valley and the red drum in South Jersey is caused by the same warming water temperatures in the last 15-plus years. Also, other kinds of fish typically found farther south are being seen with increasing frequency, such as large groups of cownose rays and other stingrays.

It is also possible that the warmer winter water temperatures are responsible for the large numbers of striped bass around the coast in recent winters. Decades ago they used to retreat south to off North Carolina during typically cold winters. In recent years they are spending the winter farther north, off Virginia, Maryland and Delaware and taking longer to migrate south of New Jersey.

In a related way, are these warmer water temperatures responsible for the decline in abundance of species that like colder water temperatures? A good example may be that of winter flounder. I am frequently told stories of large catches of adults off the bridge over Little Sheepshead Creek, but I know of only one time that happened in the last 30 years, and the angler wasn’t even sure what kind of fish it was because winter flounders are so infrequently captured. A detailed study of winter flounders from long-term trawl surveys off New Jersey by state and federal fishery biologists indicates that winter flounders are more often found farther north and offshore than they used to be, perhaps in response to warming temperatures. The same may be true of other cold water species such as Atlantic herring and pollock.

Kenneth W. Able is a marine biologist and director of the Rutgers University Marine Field Station in Little Egg Harbor. This story will be included in his forthcoming book on the underwater natural history of the Mullica Valley.

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