Author: abby

Air-breathing

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A mudskipper is an amphibious, air-breathing fish (photo credit: National Aquarium).

Guest post: Gretchen Stokes, University of Florida

Air-breathing fishes are those that respire using aerial gas exchange instead of, or in addition to, that of the water.  Air-breathing is an ancient vertebrate specialization that evolved from aquatic hypoxia (e.g., areas of seasonally flooded wetlands, under ice).  Air-breathing fishes are equipped with one or more modified respiratory structure to breathe, such as modified air bladders, lungs, skin or gills.  Some air-breathing fishes (facultative air-breathers) rely mainly on gills with supplemental gas exchange from aerial breathing when conditions are poor or it is too costly to obtain oxygen from water.  Other air-breathers (obligate) require continuous, regular surface breathing.  Yet another group of air-breathing fishes are amphibious, venturing to land either in an active or inactive state.

Air-breathing occurs in an estimated 450 species and 49 families of fishes, most of which are found in the tropics.  In North America, common air-breathing species include gar, tarpon and bowfin.  Aquarium enthusiasts may be familiar with the air-breathing habits of well-known betas.  Globally the list becomes expansive with many unique adaptations, such as lungfishes, mudskippers, snakeheads or air-breathing catfishes.  Whether a gulp of air at the water’s surface, crawling on land to feed, or maintaining a high tolerance to air exposure with specialized skin, air-breathing allows for unique adaptations and survival in extreme environments.

Fingerling

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Fingerling size fish (photo credit: Food and Agriculture Organization).

Guest post: Logan Neu, University of Minnesota Twin Cities

Fingerling is a broad term applied to a juvenile fish that is about the size of a finger.  The definition of what length classifies a fish as a fingerling varies between species, but the Food and Agriculture Organization (FAO) generally defines a fingerling as ranging in length from 10 to 15 centimeters.  The term fingerling is most often used in aquaculture and fish stocking programs because fish at this life stage are more physically developed and better equipped to survive the harsh outdoor environment than earlier life stages.  Most fish stocking programs stock fish at this life stage in order to increase the survival rate of the newly released fish.

Substrate

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Substrate in streams, rivers, lakes, and the ocean creates important fish habitat and plays an important role in multiple fish life history processes, daily activity, and prey availability. Substrate in aquatic habitats consists of surface and subsurface materials in the streambed, riverbed, or ocean bottom with different fish preferring different types of substrate.
In freshwater ecosystems, substrate is classified by particle size. For example, boulder is classified as substrate larger than 256 millimeters and very fine sand is classified as substrate between 0.0625 and 0.125 millimeters. Sea grass beds and coral reefs in ocean environments are also a very important substrate for marine fish. Fish rely on specific substrate types for spawning, predation, and shelter. For example, in Moreton Bay in Australia researchers found the double-ended pipefish, eastern trumpeter, and fan-bellied leatherjack all preferred vegetated substrate compared to bare sand substrate.
Changes in substrate can influence growth, survival, and recruitment of fish in aquatic ecosystems. Urbanization, land use, sedimentation, commercial fishing activities, and coral reef bleaching are all factors in shifting substrate habitat with potential negative impacts to fish populations.

Creel Survey

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A creel survey in action (photo credit: AFS).

Guest post: Logan Neu, University of Minnesota Twin Cities

A creel survey (also known as an angler survey) is a type of in-person survey performed by resource managers where an interviewer asks an angler questions about their fishing experience including questions such as the duration of the trip, how many fish they caught, and if they were satisfied with their experience.  The interviewer may also ask about the angler’s thoughts about a future management decision. Additionally, harvested fish are counted and measured.

Creel surveys are performed to gain insight about recreational angling perceptions, efforts, and harvests in order to inform future decision making.  Creel surveys are a valuable tool for fisheries managers to use in understanding the systems they manage and how the public interacts with them.

phylogeny

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Phylogeny of fishes (diagram credit: evolution.berkeley.edu).

Phylogeny is the representation of evolutionary relationships, often displayed as a “tree” (i.e., branching diagram) where the most closely related organisms are connected by a node and more distantly related organisms have multiple steps back in the tree before they are connected.  Nodes are often characterized by biogeographic events and evolutionary innovations.

In fishes, jawless fishes (such as hagfish and lampreys) are the most primitive, cartilaginous, and without paired fins; sharks and rays are cartilaginous with jaws and placoid denticles; and bony fish are the most diverse and derived fishes, with scales (see cycloid and ctenoid), swim bladders, and bony skeletons.

 

 

Culvert

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Three perched culverts (photo credit: USFWS).

A culvert is essentially a tunnel to pass flowing water, typically a small stream, under a man-made structure, usually a road.  Depending on the size, placement, and design of a culvert, the impacts to a stream channel vary.  These impacts, in turn, can affect fish habitat and fish migration.

Culverts are frequently barriers to fish movement.  If culverts are perched, where the outlet is higher than the elevation of the downstream water, fish are required to leap up into the culvert (if they are able) to continue moving upstream.  Often, culverts are not installed to be perched from the outset, but the situation is caused by erosion at the outlet of the culvert from high flows which scour the channel bed.  This type of culvert creates a downstream pool, changes the flow velocity and habitat type, and, consequently, can alter the fish community as well.

Local, state, and federal managers often work to replace or retrofit culverts that have significant ramifications for fish passage.  The U.S. Fish & Wildlife Service’s National Fish Passage Program is one example.

Biogeography

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Phylogeny and biogeography of liverbearers (genus Brachyrhaphis; figure credit: Ingley et al. 2015).

Biogeography is the study of patterns in distribution of fish (or other) species.  Biogeography provides an understanding of where populations are currently present and can help infer evolutionary relationships at a broad scale, including historic population isolation and colonization events.  Geologically, many species patterns can be tracked with plate tectonics.  The study of biogeography can also complement understanding of current ecological processes to explain distribution of populations at a local scale.

Please see here for more information.

Longline

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(Diagram credit: Australian Fisheries Management Authority)

A longline a type of fishing gear that is generally used to target pelagic species, such as large tuna and billfish.  Baited hooks are attached to a long fishing line via shorter branch lines called snoods or gangions.  Longlines can be anchored or freely adrift (with tracking devices so they can be retrieved).  In certain open ocean fisheries, these lines can be miles long and hold thousands of hooks.  They can be located at the surface or deeper in the water column.

Due to the nature of the gear, longlines are often subject to bycatch of unintended species.  Management strategies to reduce incidental take of sharks, birds, turtles and other species include setting the lines quickly, at deeper depths, and at night.  Sound deterrents can also help ward off seabirds.

Demersal

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Guest post: Lauren Flynn, New Mexico State University

Example of a demersal catch, painted in the 17th century. Nature morte de poissons au bord d’un ravage by Jan van Kessel the Elder, Source: Wikimedia Commons.

From the Latin verb demergere, meaning ‘to sink’, demersal describes fish that live on or just above the ocean or lake floor.  It can also refer to a commercial fishery for groundfish and shellfish, which typically uses gear that is weighted so it sinks to the bottom.  Demersal fish are frequently captured by a trawl net that drags along the ocean or lake floor.  As a result, demersal fisheries tend to be less discriminate than pelagic fishing methods such as long lines or gill nets that target fish using specific bait, specialized hooks, or mesh size.  Bycatch can be an issue for demersal fisheries, but trawl net modifications using Bycatch Reduction Devices (BRD) help to increase capture of target species and reduce unintended catch.

Examples of demersal fish species are cod, haddock, and flatfish such as turbot and halibut.  Popular shellfish include crab, shrimp, and lobster.

For comparison, see pelagic.

ITQ

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ITQ is an abbreviation for Individual Transferable Quota (image credit: Iceland Magazine).

An ITQ is an Individual Transferable Quota.  It is part of a quota system in which the managing agency divides up catch shares of the Total Allowable Catch (TAC) for the fishing season.  This essentially, creates a “stock market” like system for the fishery where ITQs can be bought and sold.

Setting up this type of management system is often contentious because some consider this process a privatization of public resources and others are concerned about the equity of the initial ITQ allocations.  Generally, the starting ITQs are based on recent records from the fishery, such as boat ownership or prior catch.  Once the system is in place, ITQs can be rented, bought, or sold.

While ITQs are considered effective in preventing “tragedy of the commons” collapses of fish stocks and have been credited with helping restore some fish populations, the approach remains controversial in some fisheries due to concerns with consolidation of ownership through market-based approaches.