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38 Cards in this Set

  • Front
  • Back
-actively swimming pelagic organisms
-mostly fishes, but can also include squid, scallops, crabs, shrimp, whales.
Typically high biomass levels
-important commercial fisheries
-seasonal in estuaries
-H.L. Menken described the Chesapeake as a great "protein factory"
-Because of economic value they are often intensively investigated
eg. blue crab life history and aquaculture
eg. disease resistance in striped bass
crab aggression is a major factor
Taxonomic considerations
-mostly fish but includes diverse invertebrates and even mammals
-in estuaries 8-15 species are 90% of the total biomass
-marine and fresh water systems have higher diversity
freshwater eels
herring-like fish
sea trout, drum, croakers
Decapod crustacea
most widespread 5 pairs of appendages
The blue crap, Callinectes sapidus
is the most important chesapeake crustacean
"The beautiful swimmers"
William Warner, won pulitzer prize
The most important invertebrate nekton
"good to eat"
Ecological or Functional Classification of Nekton
-Shallow water
Shallow water fishes
-Estuarine edges and "edge effect"
-Generally small
-No migratory behavior
-Schools of killfish and silversides are common in the bay
Pelagic Species
-Swim freely in water column
-Usually in schools near fish feeding create turbulence and an oil slick
-Usually strong migratory behavior anadromous
1. Plankton feeders-Shad
2. Carnivores-blue stripers
Plankton feeders
May specialize in phytoplankton or detritus
Alosa "alosids"
Herring and Menhaden
modified gills to filter zooplankton and phytoplankton
Carnivorous pelagic fish
-Feed on pelagic fishes, forage fish, like menhaden or herring
-bluefish Pomatomus Saltatrix
-Striped bass Monrone Saxatilis
Epibenthic or demersal
-Bottom oriented species. Often swim near bottom
-Most diverse group due to
1. Substrate variety
2. Biotic and abiotic interaction including repro. strategies, migration patters, food availability
-Catfish, flatfish, croakers, hogchoker.
Adaptations to nektonic and estuarine existence
-swimming organs
-steamlined body
-specific gravity near water
-ability to extract oxygen rapidly
nektonic adaptations
-shad have large eyes to escape predation
-anadromous fish have keen olfactory systems
-locate natal rivers by smell
-natural history of the senses.. diane ackerman
Stressful estuarine life
-fluctuating chemical and physical environment
-places energy demands on fish...salinity and osmoregulation
-many species can't adapt so the number of estuarine species is low
-however, many species spend part of their life history in an estuary..
blue crab
callinected sapidus
blue crabs information
-key component of Bay culture, economy, and cuisine
-native americans consumed crabs (midden data)
Crab life history
-Mating occurs June-October and peaks in July-August
-male joins female at pubertal molt...deposits sperm packets..."doublers"
-postcopulatory embrace for several days while female shell hardens
-sook run...fertilized females migrate to south of Bay
-females release egg mass
-eggs hatch producing planktonic zoea which drift out over continental shelf
-megalops enters and move up Bay through tidal action and salt wedge
-45 days after hatching juvenile crabs develop
-immature crabs will molt up to 20 times during their lives
-mature in 12-16 months, probably only live in 3 years
-females migrate to the souther bay in october.
soft crabs
value added product
Controlling molting
-eyestalk glands produce an inhibitor to molting
-remove eyestalks and remove inhibitor
-molt hormone is ecdysone
-soft crabs on demand
Crab shells
-made of an important biopolymer called chitin
-resistent to biological degradation
-can be induced to have a positive charge.. can be used in chemical reactions
factors contributing to blue crab decline
-fishing pressure... 90% of crabs spawning potential removed each year.. 70% may be acceptable
-water quality...
1. nutrients, algae and anoxia
2. decline of SAV
3. increased stress=increased disease
-scientists believe that reduced population levels make the blue crab more susceptible to other disturbances
-many argue that the blue crab has been exploited to near collapse
management needs for crabs
-reduced length of crabbing season
-ban winter dredging
-limit days or hours of work.
-limit commercia or recreational licenses
reduce wasteful crab harvesting
-10-30% of crab pots lost each year
-crabs enter, die and attract other crabs... self baiting.
1. biodegradable escape hatches
2. Ids on pots for accountability
3. cull rings allow small crabs to escape
-ban harvest of sponge crabs
-Ernst calls for a coordinated management between MD and VA... winter dredging plan