SCDNR Update: Winter impacts on spotted seatrout and shrimp

by | May 11, 2018 2:47 pm

Less than a week into the new year, 2018 took the Southeast by surprise with record low temperatures and up to half a foot of ice and snow. While many were out enjoying the most significant snowfall in a generation, a number of biologists and anglers were watching the mercury drop with increasing anxiety.
Many of the South’s most iconic coastal animals are warmth-loving subtropical species, which puts them in a bind when winter temperatures drop rapidly or for long periods of time. Here in South Carolina, we’ve seen our fair share of cold-stunned mammals and sea turtles in recent years, but fish and crustaceans can be vulnerable too. Two particularly important species that suffer in cold weather are the spotted seatrout (or speckled trout) and white shrimp, which respectively help form the backbones of South Carolina’s recreational and commercial fishing industries.
With heavy ice blocking roads and cyclonic winds raging offshore, it would be several days before South Carolina Department of Natural Resources biologists could get out to assess the initial effects on marine life – and much longer to fully study the long-term impacts.
In the meantime, the coastal community stepped up to help in a couple big ways, for which our staff have been very grateful.
In the days following the cold weather event, coastal South Carolinians provided 164 reports to the SCDNR about fish kills ranging from Little River to Hilton Head Island. The reports gave clues as to the severity of the impacts, where they were being felt, and which species were impacted, allowing our staff to better target their investigation. Reports of dead or cold-stunned spotted seatrout numbered the highest, but effects on everything from shrimp to sea turtles and even pelicans were also reported.
As a precautionary measure, SCDNR officials began urging anglers to practice catch and release of seatrout. The angling community responded in kind with their own catchy hashtags, public commitments, and even donations to help SCDNR better respond to the seatrout decline. But biologists could not determine exactly how severe that die-off was until they’d collected several more months’ worth of seatrout data and compared it to their historic data.
Today we have a more complete picture of the cold weather impacts on spotted seatrout and shrimp – and for seatrout, at least, the findings are more positive than expected.

Positive News for Spotted Seatrout
From January through March, our inshore fisheries team set out their trammel nets 241 times across the state’s estuaries. What they caught at first was well below normal in terms of spotted seatrout – just one seatrout per net set, on average – and the phenomenon spanned the entire coastline.
We know from decades of trammel net data that March is an important month for predicting seatrout numbers, because there’s a strong correlation between the number of fish caught per trammel net set in March and the success of the overall year. The better the numbers we see in March, the better the numbers we can expect for the rest of the year.
As it turned out, March catches of seatrout were not as poor as we feared. In short, the first quarter’s numbers suggest we’ll see slightly below-average abundance of seatrout this year – putting the population in a better position than after the winter die-off events of 2000-2001 and 2010-2011.
Numbers weren’t the only thing to worry about. Because research has suggested that larger spotted seatrout may be more vulnerable to low temperatures, SCDNR biologists were concerned that the state’s biggest and most productive trout might be especially hard hit. These mature fish contribute the most eggs to each annual ‘crop’ of seatrout, which means their loss could be felt for years to come.
Thankfully, that worry has not borne out.
“We’re still seeing a wide range of spotted seatrout sizes,” said Dr. Joey Ballenger, head of the SCDNR inshore fisheries section. His team has been seeing large seatrout (>~15 inches) in proportions similar to the 25-year average, allaying fears that the largest fish were disproportionately killed.
“Given the severity of the winter, we’re pleasantly surprised with the apparent state of the spotted seatrout resource based on the March catches,” said Ballenger. “It doesn’t seem to be as significant an event as we observed in 2000-2001 and 2010-2011. But because the picture’s still incomplete, we’re still exercising caution.”
That means SCDNR officials will continue to encourage catch and release of spotted seatrout until the end of September, when spawning season ends. After recent cold winters, the seatrout population has taken anywhere from two to five years to fully recover. By practicing catch and release now, anglers can help the seatrout population recover more quickly.
Since the cold snap in January 2018, SCDNR crustacean biologists have been reporting far fewer shrimp per trawl than average. (Photo: E. Weeks/SCDNR)

Spring White Shrimp Took a Beating
During the January cold streak, temperatures dropped below 48 degrees Fahrenheit in Charleston Harbor, an important threshold below which shrimp start to die. Charleston had three weeks of below 48 degree waters, which killed most of the shrimp overwintering in our coastal waters. SCDNR fisheries staff immediately closed state waters to trawling and requested that federal counterparts do the same in federal waters, in order to protect the shrimp remaining offshore.
Our crustacean biologists have since been closely monitoring the situation and, not surprisingly, reporting below-average numbers of white shrimp in areas such as Charleston Harbor. Because SCDNR officials do not typically open the spring trawling season until they have evidence that enough white shrimp have spawned to produce a robust fall crop, they are anticipating a later-than-average opening this year (which typically opens in full in mid- to late May).
There are two silver linings to this rather gloomy news. The first is that shrimp are prolific spawners — a single female shrimp can produce millions of eggs in a spawning season, which means that it’s too soon to write off the fall white shrimp harvest. The second bright spot is that brown shrimp, the species most commonly harvested during the summer months, were not likely impacted by the cold January. Although they make up a smaller proportion by weight and dollar value of commercial shrimpers’ harvests, brown shrimp taste just as good grilled, steamed and pickled as their white counterparts.

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