Spotty oys­ter mor­tal­ity ap­pears in Bay


Spe­cial from the Star Demo­crat

— Oys­ters in wa­ters from Til­gh­man Is­land south are turn­ing up dead, and there could be any num­ber or a com­bi­na­tion of sev­eral rea­sons why.

The mor­tal­ity is spotty, said Mary­land Depart­ment of Nat­u­ral Re­sources Shell­fish Di­vi­sion Di­rec­tor Chris Judy, but still some­thing wa­ter­men should keep an eye on and in­form the depart­ment when they pull up dead oys­ters.

DNR is con­duct­ing its fall oys­ter sur­vey. Mean­while, it has been get­ting re­ports from wa­ter­men about this oys­ter sea­son be­ing a worse har­vest year than last sea­son.

The mor­tal­ity lev­els de­pend on the bar, Judy said. A lot of ar­eas have sim­i­lar mor­tal­ity rates com­pared to last year, he said.

“We’ve been to oys­ter bars were the mor­tal­ity is well over 30 per­cent, which is high,” he said. “But in the very next bar, it looks fine.”

There are a few the­o­ries about the causes of the mor­tal­ity.

The most ob­vi­ous of which, Judy said, is it has been very dry and salin­ity lev­els are up, and have been for more than a year. High salin­ity lev­els can cause a spike in disease, and when disease in­creases, mor­tal­ity can fol­low, he said.

An­other the­ory points to low dis­solved oxy­gen in the water, which can suf­fo­cate the oys­ters.

An­other the­ory is they are dy­ing be-


cause it has been warmer than usual lately, and be­cause of that, oys­ters have been spawn­ing longer and are weak­ened for an ex­tended pe­riod of time.

“Here it is Novem­ber, and it feels like Oc­to­ber or even Septem­ber,” Judy said. “We ac­tu­ally see some oys­ters at the tail end of spawn­ing, and it’s midNovem­ber al­ready.”

When oys­ters spawn, they be­come weak, “so if you have a sit­u­a­tion where the tem­per­a­tures are in­creased late into the sea­son, they’re in a weak­ened con­di­tion,” and if they’re in­fected with disease, “you’ve got an oys­ter that is highly stressed,” he said.

They’re all com­pli­cat­ing fac­tors, but still only the­o­ries, Judy said. It won’t be known for sure what ex­actly is hap­pen­ing un­til the fall sur­vey is fin­ished and re­sults are re­leased in mid-De­cem­ber and lab­o­ra­tory disease test re­sults come in, which Judy said should hap­pen shortly af­ter the sur­vey re­sults are re­leased.

“The pieces of the puz­zle fit to­gether, but the prob­lem is you can­not pre­dict this is go­ing to hap­pen,” Judy said.

It’s not the first time Mary­land’s oys­ters have been con­fronted with po­ten­tial disease. The last dras­tic drop in the state’s oys­ter pop­u­la­tion came af­ter disease hit it hard in 1999.

A bad spat set that year led to less oys­ters to har­vest a few years down the road, and land­ings were at their worst in Mary­land his­tory dur­ing the 2003-04 oys­ter sea­son, when Mary­land wa­ter­men caught a lit­tle more than 25,800 bushels, com­pared to about 413,000 bushels in the 1998-99 sea­son and about 370,800 the sea­son af­ter that, ac­cord­ing to DNR fig­ures.

The last strong spat sets were in 2010 and 2012, Judy said. Strong spat sets will yield more har­vestable oys­ter later on when they grow to mar­ket size in a few years, which is why Mary­land re­cently had sev­eral good years of har­vest.

Since 2010, har­vest peaked dur­ing the 2013-14 sea­son, when Mary­land wa­ter­men landed more than 431,000 bushels.

But since 2012, spat set has been low. As a re­sult, har­vest is now in de­cline, Judy said.

“The Mary­land oys­ter fish­ery is highly de­pen­dent on the level of spat set,” he said. “Fa­vor­able set rates will in­crease the har­vest and low set rates will de­press the har­vest.”

Land­ings dipped back into the 300,000s in the 2014-15 sea­son, and Mary­land wa­ter­men landed more than 374,000 bushels last year.

Land­ings are ex­pected to de­cline again this year, Judy said, which is some­thing DNR has been hear­ing from wa­ter­men through­out the sea­son so far.

Judy said if any wa­ter­men are see­ing dead oys­ters in the water, they should mark down the name of the bar and the trib­u­tary. He asked wa­ter­men to pro­vide that in­for­ma­tion to DNR, so sci­en­tists can get a clearer pic­ture of what’s hap­pen­ing and where it’s hap­pen­ing. Any in­for­ma­tion can be re­layed to DNR by call­ing 410-260-8259.

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