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38 Cards in this Set
- Front
- Back
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Nekton
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-actively swimming pelagic organisms
-mostly fishes, but can also include squid, scallops, crabs, shrimp, whales. |
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Typically high biomass levels
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-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 |
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Morphology
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eg. blue crab life history and aquaculture
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Physiology
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eg. disease resistance in striped bass
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Ethology
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crab aggression is a major factor
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Taxonomic considerations
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-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 |
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Anguillidae
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freshwater eels
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Clupeidae
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herring-like fish
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engraulidae
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anchovies
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Sciaenidae
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sea trout, drum, croakers
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seranidae
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bass
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Decapod crustacea
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most widespread 5 pairs of appendages
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The blue crap, Callinectes sapidus
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is the most important chesapeake crustacean
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"The beautiful swimmers"
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William Warner, won pulitzer prize
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Crustacea
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The most important invertebrate nekton
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Sapidus
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"good to eat"
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Ecological or Functional Classification of Nekton
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-Shallow water
-Pelagic -Epibenthic |
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Shallow water fishes
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-Estuarine edges and "edge effect"
-Marshes -Grassbeds -Tidepools -Generally small -No migratory behavior -Schools of killfish and silversides are common in the bay |
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Pelagic Species
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-Swim freely in water column
-Usually in schools near surface...blue fish feeding create turbulence and an oil slick -Usually strong migratory behavior anadromous 1. Plankton feeders-Shad 2. Carnivores-blue stripers |
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Plankton feeders
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May specialize in phytoplankton or detritus
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Herring--
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Alosa "alosids"
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Anchovies
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Anchoa
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Menhaden
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Brevoortia
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Herring and Menhaden
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modified gills to filter zooplankton and phytoplankton
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Carnivorous pelagic fish
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-Feed on pelagic fishes, forage fish, like menhaden or herring
-bluefish Pomatomus Saltatrix -Striped bass Monrone Saxatilis |
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Epibenthic or demersal
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-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. |
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Adaptations to nektonic and estuarine existence
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-swimming organs
-steamlined body -specific gravity near water -ability to extract oxygen rapidly |
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nektonic adaptations
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-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 |
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Stressful estuarine life
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-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.. |
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blue crab
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callinected sapidus
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blue crabs information
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-key component of Bay culture, economy, and cuisine
-native americans consumed crabs (midden data) |
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Crab life history
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-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. |
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soft crabs
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value added product
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Controlling molting
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-eyestalk glands produce an inhibitor to molting
-remove eyestalks and remove inhibitor -molt hormone is ecdysone -soft crabs on demand |
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Crab shells
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-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 |
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factors contributing to blue crab decline
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-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 |
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management needs for crabs
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-reduced length of crabbing season
-ban winter dredging -limit days or hours of work. -sanctuaries -limit commercia or recreational licenses -limits |
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reduce wasteful crab harvesting
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-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 |
