T

TAC

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TAC is an abbreviation for Total Allowable Catch (image credit: mimiculture.com; icon design: Scott de Jonge from Flatiron).

TAC is Total Allowable Catch.  This is the upper limit in the amount of fish, either by weight or number, that a fishery is allocated in a given season or year.  TACs can apply to the targeted fish and/or bycatch, where once the limit is reached the fishery is closed for the remainder of the applicable time frame.  Often, the TAC is set based on an assessment of the stock status for the fishery, such as maximum sustainable yield (MSY).

In open-access or “derby” style fisheries, there is a free-for-all competition until the TAC is exhausted.  This can lead to risky or unsafe behavior, where vessels may continue to operate in hazardous conditions in order to harvest a larger proportion of the TAC.  In order to avoid accidents from such situations, some fisheries have opted for quota-based management systems where the TAC can be divided into catch shares, such as Individual Transferable Quotas (ITQs).

Trap, pound, and fyke nets

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Trap net (image credit: Michigan Sea Grant).

A trap or pound net is a type of fishing gear with a complex organization of nets anchored to the substrate that “lead” or funnel fish into a final compartment (i.e., trap or pound) from which they cannot escape.  In the Laurentian Great Lakes, this type of fishing gear is called a trap net and in marine and estuarine systems, it is generally called a pound net.  A fyke (pronounced similar to “like”) is specific kind of trap net that uses a series of cone-shaped bags; it is typically a smaller size.

Fish harvested from this type of gear are often considered higher quality than those harvested from gill nets because fish can swim freely in the trap/ pound until the fishermen come to haul the nets.  Certain types of bycatch can also be more readily released unharmed from this gear than others.

For an example of how this fishing gear is used, please visit “Know Your Nets” from Michigan Sea Grant.

Tubercles

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Breeding tubercles (photo credit: G. Engman and P. Cooney).

Tubercles are skin nodules made of keratin, the same materials as hair, hooves, and fingernails.  They are present on species representing at least 15 families of fishes, including even pet goldfish.  In many species, tubercles are found only on males during the breeding season and are shed shortly there after.  They are often called breeding tubercles for that reason.  The main functions for tubercles include species recognition, fighting and defense of spawning territory or nests, and stimulation of breeding females.

For more information, please see “Breeding tubercles and contact organs in fishes: their occurrence, structure, and significance” (Wiley and Collette 1970) and the related Fisheries Blog post: “Top 10 Weirdest Things Found on a Fish’s Head.”

Trophic levels

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Marine trophic levels (diagram credit: University of Waikato).

Trophic levels are a defined by the position of organisms in a food chain or food web.  The different levels help define the flow of energy within an ecosystem.  The lowest trophic level is primary producers, such as algae and phytoplankton, which generate their own energy from the sun via photosynthesis.  Primary consumers, such as herbivorous zooplankton, must eat primary producers as their source of energy.  As a general rule, each trophic level up equates to capturing 10% of the energy from the trophic level below it (e.g., a juvenile fish uses 10% of the energy it gets from eating zooplankton and only 1% of the energy the zooplankton gets from eating phytoplankton).

Many food webs contain organisms, such as fish that eat other fish and zooplankton, that do not fall into simple trophic level constructs.  Stable isotope analyses can be used to infer diet and trophic level for these complex diets by comparing isotopic signatures in tissue from the organisms of interest to those from samples of known origin.  Commonly used isotopes for aquatic ecosystem food web analyses include 13C, 15N and 34S.

T & E species

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Atlantic Salmon are an endangered species protected by USFWS and NOAA in the U.S.

T & E is an acronym for threatened and endangered.

These are both status metrics for risk of extinction.  Endangered species are considered on the “brink of extinction” throughout their range and threatened species are likely to become endangered in the near future.

The species that are on this list in the United States receive certain protections under the Endangered Species Act of 1973 which recognizes the “esthetic, ecological, educational, historical, recreational, and scientific value [of these species] to the Nation and its people.”  The U.S. Fish and Wildlife Service (USFWS) and the National Oceanic and Atmospheric Administration (NOAA) are mandated to protect the T & E fish species, such as Atlantic Salmon (Salmo salar), among other aquatic and terrestrial species that fall under their jurisdictions.

Thermoregulation

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Fish don't sweat to regulate their body temperature but they do have strategies for thermoregulation (www.fishlady.us).

Fish don’t sweat to regulate their body temperature but they do have strategies for thermoregulation (www.fishlady.us).

Thermoregulation is the process by which an organism controls its internal temperature.  Fish have many different mechanisms for regulating their temperature.  Most fish are ectothermic, using their environmental temperature to manage their body temperature, but some fish are endothermic, having the metabolic ability to internally manage temperature.  Poikilothermic fish are ectotherms which have no control over their body temperature; their core body temperature conforms to ambient temperature.  Eurythermic fish have evolved to survive in a wide range of environmental temperatures and stenothermic fish have evolved to survive in a narrow range of environmental temperatures.

Thermoregulation is very important for fish because temperature influences the function of many organs and the rate of many metabolic processes.  Most fish species have evolved to survive within a specific temperature ranges; outside that range, enzymes can degrade, organs can fail, and the organism can die.  Understanding thermoregulation for fish species is particularly important when considering implications for climate change.

 

Teleost

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A Slingjaw Wrasse is an extreme example of a teleost's protrusible jaw

A Slingjaw Wrasse is an extreme example of a teleost’s protrusible jaw.

Teleosts are the most diverse group of fishes (over 26,500 extant species).  Over half of all living vertebrate species are teleosts.  Teleosts are characterized by a protrusible jaw (musculature gives them the ability to move their maxilla and premaxilla) and a symmetrical tail (their spine that ends at the caudal peduncle unlike, for example, sharks).  Teleosts are estimated to have evolved during the Triassic period. By the end of the Cretaceous, the fossil record shows that teleosts dominated both freshwater and marine habitats.

TED (Turtle Excluder Device)

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TEDs significantly reduce turtle bycatch

TEDs significantly reduce turtle bycatch

Turtle Excluder Devices (TEDs) are a specific type of bycatch reduction device (BRD) that are a modification to a trawl net to keep turtles, which are not targets of the fishery, from being caught in the net.  TEDs are generally composed of a set of bars over the trawl net.  While small target animals, such as shrimp, pass easily between the bars into the trawl net, larger animals, such as turtles or even sharks, can escape through a side opening in the net after they have hit the grid of bars.  TEDs were developed to eliminate turtle mortality from trawl fisheries.  Because turtles and other bycatch, or non-target catch, species often come from threatened or endangered populations, the fisheries had strict regulations on how much bycatch was allowed.   TEDs, by reducing bycatch, allows the shrimp trawls to operate more with more ecological and economic efficiency.

For more information, please visit: http://www.fisheries.noaa.gov/pr/species/turtles/teds.htm