Hats for ALL crew who participate … and jacket lottery draw to be awarded to 3 vessels.

IPHC sex mark hat 2IPHC sex mark hat 1

We are asking for your assistance in marking fish as either male or female while dressing them at sea, so that the port samplers can add sex information from the Pacific halibut that they sample to the length and age data that they routinely collect.

Accurately estimating female spawning stock biomass is one of the main objectives of the IPHC’s assessment process. The current lack of information on the sex ratio of the commercial catch represents one of the major sources of uncertainty in our estimates of female abundance. Therefore, knowledge of the sex ratio of the commercial catch will substantially increase the precision of the stock assessment. Monitoring changes in the sex ratio of Pacific halibut on fishing grounds over the course of each year and from area to area would also improve our understanding of how migration occurs. We are currently unable to make full use of the greatest source of data that exists – commercially harvested Pacific halibut – to answer these questions because the fish are dressed at sea.

Over the past few years, we have collaborated with commercial fishermen to develop a simple method for marking halibut according to sex while dressing using the identification cuts that are described here.

First: Determine whether you have a female or a male halibut.

Pacific halibut gonads

Then: Mark the fish as either female or male, using your gutting knife.

Knife cut diagram

Female: Make two parallel cuts through the top (dorsal) fin (see photo below, left), being sure to make your cuts using an upward stroke, away from the body, to avoid damaging the flesh. Two (2) cuts must be made, so that the sex marks cannot be confused with pre-existing injuries to the fin. Note that only the top (dorsal) fin can be marked; any marks found in the lower fin will be ignored when the fish is sampled in port.

Male: Make a single cut through the gill plate (operculum) on the fish’s white side (see photo below, right). Make the cut using an upward stroke, making the cut parallel to the rear edge of the gill plate. The cut should extend about 3/4 of the way up the gill plate, so the “flap” that you create will remain attached to the plate.

Pacific halibut gonads

Please mark 100% of your catch!

(If you forget or cannot mark some, still mark the rest)

Your efforts will directly contribute to our understanding and to the management of this valuable resource!

See our Sex-marking FAQs Page