Author: abby

Caudal fin

Posted by on Leave a Comment
A caudal fin graced the Summer 2012 cover of Eddies magazine (fws.gov/eddies)

A caudal fin graced the Summer 2012 cover of Eddies magazine (fws.gov/eddies)

The caudal fin, or tail, of a fish is the only fin to be connected to the vertebral column.  It is the primary means of locomotion for most fish.  Unlike many marine mammals with tails that use an up-and-down motion, fish generally use a side-to-side thrust of their caudal fin for propulsion.  The shape of the caudal fin can be indicative of the style of motion for a fish.  For example, very fast swimming fish like tunas have lunate caudal fins for more efficient swimming while lie-in-wait predators like grouper have a strong, wide base of the tail, the caudal peduncle, for faster acceleration.

Caudal fin come in many shapes and sizes; form often follows function

Caudal fins come in many shapes and sizes; form often follows function

Adipose fin

Posted by on Leave a Comment
The adipose fin may serve as a "precaudal flow sensor"

The adipose fin may serve as a “precaudal flow sensor”

The adipose fin is a small fleshy fin found posterior to the dorsal fin and anterior of the caudal fin.  It is only found on few fish, including trout, salmon, and catfish.  When it was named, it was thought to hold fat, or adipose, tissue.  Once this hypothesis was disproved, fisheries biologists long considered this fin to be “non-functional.”  More recently, research suggests that the adipose fin may serve as a “precaudal flow sensor” to improve maneuverability in turbulent waters.  This new research may raise concerns because adipose fin clipping is commonly used to “tag” hatchery reared salmon to distinguish them from wild salmon for catch and release management purposes.

For more information on the adipose fin, please visit: http://thefisheriesblog.com/2013/05/28/the-adipose-fin-old-mysteries-with-new-answers/

Pelagic zone

Posted by on Leave a Comment
The pelagic zone is divided into layers based on light

The pelagic zone is divided into layers based on light

The pelagic zone is the region of a body of water (lake, river, or ocean) that is not associated with the bottom (see benthic zone) or shore (see littoral zone).  This habitat zone is truly a three dimensional habitat space.  Some fish that occupy the pelagic zone never encounter the bottom or shore throughout their lives.  Because the pelagic zone is a nutrient poor environment, large fish have two basic strategies to get meals – either swim long distances in search of nutrient-rich prey (like many oceanic sharks and tunas) or drift with currents and eat nutrient-poor prey (like the Ocean Sunfish Mola mola).  The pelagic zone is divided into zones based on light penetration from the surface:

  • Epipelagic (sunlight; 0-200m)
  • Mesopelagic (twilight; 200-1,000m)
  • Bathypelagic (no light; 1,000-4,000m)
  • Abyssopelagic (4,000m – ocean floor)
  • Hadopelagic (deep sea trenches)

Benthic zone

Posted by on Leave a Comment

The benthic zone is region of a body of water (lake, river, or ocean) that is near the bottom.  It includes the surface and some of the sub-surface layers of the sediment.  The sediment can sand, mud, rocks, coral, among other substances.  Benthos are organisms living in the benthic zone.  These organisms are predominately invertebrates, but the benthic community is very important to some fish species.  For example, the tripod fish (Bathypterois grallator) is a deep-sea benthic fish that uses modified fins and fin rays to stand on the ocean floor and wait for prey items to approach.  These fish can grow up to 3 feet long!

Tripod fish use the benthic zone to feed

Tripod fish use the benthic zone to feed

Littoral zone

Posted by on Leave a Comment

The littoral zone is the region of a body of water (lake, river, or ocean) that is near the shore.  While there is no exact definition of the zone, in marine systems it is generally considered to extend from the high-water mark to the continental shelf; freshwater systems it is generally considered to be wetland zones where sunlight can still reach rooted plants.  Because of its close association with terrestrial systems, the littoral zone is nutrient rich and highly productive.  Fish in these areas, like coral reef fishes, for example, often become highly specialized feeders because of the diverse and abundant food sources.

littoral zones are nearshore

littoral zones are nearshore

IUU fishing

Posted by on Leave a Comment
Portuguese naval officers and Gabonese sailors inspect a holding bay for fish aboard an illegal fishing vessel.

Portuguese naval officers and Gabonese sailors inspect a holding bay for fish aboard an illegal fishing vessel.

IUU fishing is illegal, unregulated, and unreported fishing.  According to the 2001 FAO International Plan of Action to Prevent, Deter and Eliminate Illegal, Unreported, and Unregulated Fishing,

Illegal fishing refers to activities:

  • conducted by national or foreign vessels in waters under the jurisdiction of a State, without the permission of that State, or in contravention of its laws and regulations;
  • conducted by vessels flying the flag of States that are parties to a relevant regional fisheries management organization but operate in contravention of the conservation and management measures adopted by that organization and by which the States are bound, or relevant provisions of the applicable international law; or
  • in violation of national laws or international obligations, including those undertaken by cooperating States to a relevant regional fisheries management organization.

Unreported fishing refers to fishing activities:

  • that have not been reported, or have been misreported, to the relevant national authority, in contravention of national laws and regulations; or
  • undertaken in the area of competence of a relevant regional fisheries management organization which have not been reported or have been misreported, in contravention of the reporting procedures of that organization.

Unregulated fishing refers to fishing activities:

  • in the area of application of a relevant regional fisheries management organization that are conducted by vessels without nationality, or by those flying the flag of a State not party to that organization, or by a fishing entity, in a manner that is not consistent with or contravenes the conservation and management measures of that organization; or
  • in areas or for fish stocks in relation to which there are no applicable conservation or management measures and where such fishing activities are conducted in a manner inconsistent with State responsibilities for the conservation of living marine resources under international law.

While all three types of IUU fishing result from a lack of resources (to enforce, report, and regulate), lumping these three different types of fishing under one category simplifies the complex issues, linking illegal activities (i.e., illegal fishing) with legal activities (i.e., unreported and unregulated fishing).  Illegal fishing is a regulatory issue; unreported and unregulated fisheries do not break any law – they are management issues, or rather a lack of management issue.  IUU fishing often basks in a negative light, but this legal distinction makes it difficult to chastise fishermen just because their government lacks the capabilities to report or regulate their fishery.  For more information on the challenges to managing IUU fishing, please refer to the following AFS publication:

Serdy, Andrew.  2011. Simplistic or Surreptitious? Beyond the Flawed Concept(s) of IUU Fishing.  Pages 253-279 in W.W. Taylor, A.J. Lynch, and M.G. Schechter, editors.  Sustainable Fisheries: Multi-Level Approaches to a Global Problem.  American Fisheries Society, Bethesda, Maryland.

American Fisheries Society FACEBOOK logo AFS American Fisheries Society on Google Plus logo American Fisheries Society AFS logo on LINKEDIN American Fisheries Society on Twitter AFS Logo American Fisheries Society on Pinterest AFS logo

 

Ichthyology

Posted by on 1 Comment
Ichthyology is the study of fishes

Ichthyology is the study of fishes

Ichthyology is the study of fishes*.  With an estimated 27,977 species, fish are the most numerous and diverse group of vertebrate species.  In fact, there are more fish species than all other groups of vertebrates (amphibians, reptiles, birds, and mammals) combined.

One could argue that people have been studying fish for the purposes of food since prehistoric times, but the scientific study of fish began in earnest during the European Renaissance.  While famed taxonomist Carolus Linnaeus did identify many fish species, his colleague, Peter Artedi, is considered the “father of ichthyology” for standardizing morphometric (measurement ) and meristic (count) methods still used to classify species.  According to FishBase, a comprehensive, publically accessible database of fish species , over 10 species are named in his honor.

Beginning with basic anatomy and systematics (study of evolutionary relationships among fishes), ichthyology has broadened to include ecology (study of interactions between fish and their environment), physiology (study of internal function of fish), and behavior.  Ichthyology forms the foundation of fisheries science which applies the understanding of fishes in the context of fisheries (the harvest of fish and other aquatic organisms for human use).

 *Note that fish is singular and plural when in reference to a single species.  Fishes is plural in reference to more than one species.

American Fisheries Society FACEBOOK logo AFS American Fisheries Society on Google Plus logo American Fisheries Society AFS logo on LINKEDIN American Fisheries Society on Twitter AFS Logo American Fisheries Society on Pinterest AFS logo