Why is ageing fish important?
Ageing fishes is a vital part of fish stock management. Ageing is also important for the monitoring of fish populations and their reaction to environmental impacts such as fishing, natural mortality, and predation. This management will help aid in more long term monitoring and management of fish stocks to create sustainable fish stocks.
Our sample area focuses on two survey areas of the Chesapeake Bay and the Northwest Atlantic Ocean from Cape Hatteras, North Carolina to Martha’s Vineyard, Massachusetts. The Chesapeake Bay is the east coast’s largest estuary which makes it an essential body of water to monitor. This coupled with the near shore survey in the Atlantic provides sample coverage for many commercially valued species which should all be carefully monitored.
Age and Growth laboratory supplies
A variety of methods are used to age fish. Scales, vertebrae, spines, opercula and otoliths are a few of the hard calcified structures that are commonly used to age fish. Scales and otoliths, the fish’s ear bones, are the two most common that our group samples. Appropriate hard parts for ageing (otoliths, vertebrae, opercula or spines) are removed from each fish that is subsampled and brought back to VIMS for further analysis. Ageing structures are prepared according to methodology established by the NEFSC, Old Dominion University, and VIMS.
Typically, one otolith is selected and mounted on a piece of 100 weight paper with a thin layer of Crystal Bond. A thin transverse section is cut through the nucleus (core or focus) of the otolith, perpendicular to the sulcal groove, using two Buehler diamond wafering blades with approximately a 0.4-0.5mm spacer and a low speed Buehler Isomet saw. The resulting section is mounted on a glass slide and covered with Crystal Bond. If necessary, the sample is wet-sanded to an appropriate thickness before being covered. Some smaller, fragile otoliths are bifurcated and wet sanded to the appropriate thickness. Few particular species are read using the whole otolith. Sectioned otoliths are most commonly viewed using transmitted light under a dissecting microscope, while whole otoliths are viewed with reflected light on a black back-ground under a dissecting microscope. Other structures such as vertebrae, opercula, and spines are processed and read using the standardized and accepted methodologies for each. For all hard parts, ages are assigned as the mode of three independent readings. Ages are adjusted by a senior reader as necessary to account for the timing of sample collection and annuli deposition (mark formation). Any discrepancy amongst the three readers are flagged by the senior reader read a second time.
The samples processed allow us to determine the age of the fish when it was caught. With this data, we can get a clear picture of the age structure of the population present in the Chesapeake Bay, nearshore mid-Atlantic and southern New England.
VIMS MRG is one of the many contributors from across the United States Atlantic Coast and Gulf of Mexico that led to this cooperative and joint Ageing Manual Handbook with the ASMFC and GSMFC. The Handbook covers a broad range of managed species, processing protocols, and ageing criteria for these species.