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Age, Growth, and Maturity of Kelp Greenling
The kelp greenling (Hexagrammos decagrammus) inhabits nearshore kelp beds and rocky reefs to a depth of 150 feet. Partly due to their proximity to shore, they are highly sought after by anglers, spear fishermen, and commercial fishermen. According to Recreational Fishery Information Network data, a total of 288,000 angler trips were expended by nearshore anglers targeting kelp greenling in 2008.
Despite their importance in the California recreational fishery, we have very little information regarding kelp greenling population dynamics. A 2006 greenling stock assessment was not accepted by management due to limited scientific data. Specifically, there was uncertainty regarding greenling age, growth, mortality rates and abundance estimates.
In 2007, CDFW initiated a study to more comprehensively determine age, growth, and maturity of kelp greenling by examining sectioned otoliths, small bones used to age fish, and gonads from a larger number of individuals over a wide size range and multiple locations.
Age and Growth
Kelp greenling were collected by spearfishing while diving and hook-and-line fishing from shore. Samples were collected from Carmel Bay and Fort Bragg. Fish total length, weight, sex, maturity state, gonad weight, and liver weight were recorded. Otoliths were removed and embedded in epoxy resin prior to sectioning. Sectioned otoliths were then mounted on glass slides and wet-sanded to enhance the resolution of growth zones. Otoliths develop these growth zones as the fish ages, much like growth rings visible in the cross section of a tree trunk. Polished otoliths were viewed under a dissecting microscope and the number of opaque bands (dark bands) counted to determine the fish's age.
Maturity and Reproduction
Digital photos were taken of testes and ovaries to document maturity and reproductive status. A maturity stage classification from 1 (immature) to 5 (resting) for male greenling and 1 (immature) to 4 (resting) for female greenling was determined for each fish.
Sampling locations where kelp greenling were collected from December 2007 to February 2009.
Sectioned kelp greenling otolith viewed under dissecting microscope.
Findings to Date
- Since August 2007, project staff and volunteers have collected a total of 357 kelp greenling through monthly sampling.
- 142 females from 126 - 411 mm total length (TL)
- 215 males from 116 - 391 mm TL
- An adequate number of male greenling over 20 cm TL have been collected. Therefore, divers are now concentrating effort on collecting females and smaller males (less than 20 cm TL).
- No significant difference in length was found between left and right otoliths.
- Project staff continue to mount, section, polish and read otoliths. Twenty otoliths have been sectioned and polished to date.
- Maturity data collected by project staff indicate that kelp greenling spawn from September to January.
- Age data analysis is currently underway. Stay tuned!