Chesapeake Bay Shellfish Fisheries Flashcards
What is the highest revenue shellfish in C-Bay?
Blue Crab
Oysters
Sea Scallops
Eastern Oyster Scientific Name
Crassostrea virginica
Crassostrea virginica growing range
Canada to northern South America
Crassastrea virginica food
Phytoplankton
How do eastern oysters form reef structures?
Aggregate - pinpoints the importance of a hard substrate
Eastern Oysters size and age
Grow to ~20 cm (larger north) and maximum age of 20-25 yrs
However, it is currently rare to find an animal over 4-5 years old. Most of the population is made up of 1-4yr olds.
Eastern Oyster Environmental Tolerance
Salinity: 5 – 40 psu
Temperature: 2 - 36 ºC
Eastern Oyster Sex and rough age of maturity
Protandric hermaphrodites (male first) – mature age 1.
Eastern Oyster’s Spawning characteristics
Broadcast spawn
External fertilization
Spawn late spring through early fall (can spawn multiple times per season).
Female fecundity can produce up to 100 million eggs (20-30 million per spawn).
Eastern Oyster Fishery
- Large fishery in 1800s through mid-1900s
- Decimated by two diseases (MSX and Dermo)
Historical Fishing Gear Types
Patent tongs
Oyster dredge/oyster scrape
Hand tongs
Scientific name for MSX
Haplosporidium nelsoni -
History of MSX in the Bay
- Known since 1957 in Delaware Bay and 1959 in Chesapeake Bay
- Evidence suggests that Haplosporidium nelsoni was introduced to the US East coast with shipments of the Pacific oyster C. gigas
Characteristics of MSX
Parasitic protist that is the agent of “MSX” disease.
An acute disease from early summer to fall (May-November), where salinities > 15 psu. Intolerant of salinities below 10 psu.
Complex life cycle unresolved. Role of oysters in life cycle isn’t clear
The scientific name for dermo
Perkinsus marinus
History of Dermo
- Known since the 1940s in the Gulf of Mexico and Chesapeake Bay.
- Drought occurred in the 80’s that persisted for a decade to a decade and a half increasing the salinity in ches-bay. This allowed Dermo to transit more prolifically.
Dermo Characteristics
- Agent of “dermo” disease, apicomplexan protozoan or basal dinoflagellate.
- A wasting disease of the late summer and fall (August-November), salinities > 12-15 psu. However, can persist through long periods of very low salinity.
- Directly transmissible among oysters. Acquired during feeding, released upon defecation, death/disintegration.
What is one main reason for the increase in stock in the past ten years?
Management has moved to rotational harvest paired with shell repletion on public grounds.
After harvesting, the beds lie fallow for two years until harvesting.
What are some other management strategies in the oyster fishery today?
- Annual estimates of abundance
- License limit
- Gear type and time restrictions
- Oyster sanctuaries
- Restoration to increase the footprint of extant reefs
- Stock Management Advisory Committee
- Private Grounds
- Spat on Shell
- Increased interest in containerized aquaculture
Characteristics of Private Grounds (leases) of Oysters
Traditional ”culture” methods (been in use since early 1900s)
Shell plants to catch natural set.
Seed movement from one area (often public) to the bottom is more suitable for grow-out.
Spat on Shell
hatchery produced spat set on clean shell, planted on bottom for grow out then harvested by traditional methods.
Increase in catch on Public Grounds beginning in the mid to late 2000s. Potential contributing factors?
- Epizootic period in mid 2000s, surviving oysters exhibiting tolerance to Perkinsus
-Increased recruitment beginning in ~2008-2010 period
-Strategy of rotational harvests implemented in 2007 (Rappahannock), other rivers in later years
What is the biggest impediment for an increase oyster population
Oysters used to live to 20-25 years (need oysters to live long and die big to contribute to shell base)
-Rare to find > 4 or 5 yr old (high mortality before entering fishery – NOT fishing or disease related)
Illegal harvesting has become more prevalent in recent years with the increase in the population
Scientific Name for Atlantic Sea Scallop
Plactopecten magellanicus
Sea Scallop Biology
Distributed from Gulf of St. Lawrence (Canada) to Cape Hatteras
Occurs at depths from 20–120 m
Max age ~ 20 years
Max size ~ 9 inch shell height
Sea Scallop Life Cycle
Planktonic (~40 days, Tº dependent)
Egg -> trochophore -> veliger -> pediveliger
Settlement
~0.25 mm shell height attach to any hard substrate with byssus threads
~5 – 12 mm shell height move to bottom debris
How to identify between male and female sea scallops?
Females have red gonads
Atlantic Sea Scallops Spawning Characteristics
Separate sexes
Females can mature in 1st or 2nd year w/limited egg production
Age 4 female (85–90 mm) with ~ 2 million eggs (250 million lifetime)
Spawn in fall (also a spring spawn in Mid-Atlantic)
Georges Bank gyre entrains larvae (recruitment success related to tightness of gyre)
What factor makes it difficult to age Atlantic sea scallops?
Two spawning times ( on in fall and in spring)
Sea Scallop Fishery
Most valuable wild scallop fishery in the world
Most valuable fishery in Virginia (more recent years toss-up with oysters)
In 2007, the most valuable single species in the U.S.
58.5 million lbs. landed (~2.3 million lbs landed in 2021)
$385 million ex-vessel
What is the main gear type for Atlantic Scallop Fishery?
Scallop Dredge
Scallop Fishery Management
limited access program implemented
Effort reductions (days at sea)
Limitations on crew size
Gear restrictions (increase in cull ring size 3.0” -> 3.25” -> 3.5” -> 4.0”)
Georges Bank Groundfish Closure 1993-1999
Georges Bank Groundfish Area Closure
Groundfish was being overfished and completely closed the fishery. They found that the animals in the large-scale classes were still not there outside the closure area. Within the closure area, they were finding the larger size classes. This led to the rotational grazing practice that is now implemented with the oyster fishery in Ches-bay.
What are some unique features of the scallop industry that differ from other shellfish fisheries?
puts a certain amount of money into a pot every year to provide money for researchers. To help them make informed decisions.
Scallop fisheries – all vessels have vessel monitoring systems. Must have them turned on when they leave the dock.
The fishery (in terms of the big players) the fishery is much smaller. Easier to mange.
Scientific Name for Blue Crab
Callinectes sapidus
Blue Crab Biology
Range throughout western Atlantic (Nova Scotia to Argentina)
Tolerate wide range of temperatures, prefer estuarine salinities
Adult blue crab diet includes bivalves (hard clams, oysters), fish, crabs (including blue crabs), shrimp, plant matter, detritus, etc
Important prey & predator in the Bay
Relatively short lived: females to ~2 years, males to ~3 years
Blue Crab Spawning Characteristics
Mating occurs May to Oct in brackish water (upper Bay) when female soft (final molt)
Males protect females, but females can have multiple mates (Wells et al. 2017)
Females store spermatophore
Females produce ~1,000,000 – 5,000,000 eggs/spawn
Females move toward mouth of Bay
If late in the season, ovulation will be delayed until following spring
Crabs bury into sand and are dormant during winter
Blue Crab Fishery
Chesapeake Bay with ~1/3 of U.S. blue crab catch
Pot fishery (typically March-November)
Winter Dredge fishery (current moratorium)
Peeler crab/soft shelled crab fishery
Recreational fishery
Estimated to be 8% of total harvest (male only in MD)
Blue Crab Spawning Sanctuary
Most of c-bay is closed may 16-sept 15 for recreational and commercial harvest
Small portion of the mouth of C-bay and along the Atlantic coast is closed from may 16- sept 15 for commercial harvest
Blue Crab Stock Challenges
Since 45-55% of crabs are harvested annually – causes issues in the population.
Temp increase – lose more SAV
Dead zones (loss of food)
Blue Crab Management (Chesapeake Bay Stock Assessment Committee)
CBSAC uses winter dredge survey as primary indicator of stock status
2011 assessment implements management targets focused on the number of spawning age (1+) females as opposed to total number of crabs
2011 w/ highest total number of crabs since 1990s
2015 - started to manage the fishery based on female abundance
2017 set new (updated) biological reference points
Blue Crab Stock Status
In 2022 abundance of both mature male and females decreased and juvenile abundance remained low.
2022 results suggest that the blue crab stock is not overfished.
However, the reduced abundances, low recruitment and higher male exploitation rates are of concern.
