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Yaquina Bay Crab Research
Yaquina Bay Crab Research

Recreational crabbing

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Bay crab research

In 2003, the Oregon Legislature enacted a new sport shellfish license requirement with all resulting revenues dedicated to enhance enforcement of shellfish regulations (Oregon State Police), public health (Oregon Department of Agriculture) and management, monitoring, research and public education (Oregon Department of Fish and Wildlife (ODFW)).

ODFW is using these revenues to re-establish a shellfish program that will, in part, monitor and assess the recreational crab fishery. In 2006, ODFW’s Marine Resources Program in Newport began catch and effort surveys for the recreational crab fisheries in Yaquina and Alsea Bays.

In addition to these efforts, Newport shellfish staff began a sampling project in Yaquina Bay in May, 2007 to collect more specific information about the bay crab resource. The goal of this research is to further our understanding of the recreational crab resource and factors affecting the sustainability of this resource.

The Yaquina Bay crab sampling project is a small part of a larger, multi-year bay crab monitoring and assessment project and was designed to assess and characterize the following factors: temporal and spatial distributions of species compositions, quantities of crab, size distributions, width/weight relationships, sex ratios, shell conditions, microsporidian infection rates, and estuarine environmental factors affecting bay crabs.

 Bay crab sampling

When sampling takes place

Bay crab sampling began in May 2007. From May through September sampling took place 3 times per month. Each sampling day was a weekday to reduce interference with recreational crabbers.

Bay crab sampling
Bay Crab Sampling

The process

retrieval

Each sampling day, three recreational sized crab pots are set in 4 pre-defined areas in strings parallel to the channel. In each area: salinity, dissolved oxygen and temperature at depth is recorded. Each pot is pulled three times, for a total of 36 retrievals/ sampling day.

research

Once the pot is on deck, all crab are removed and placed in labeled buckets to be sampled.

species
Species

Identification

Each crab’s species and gender are identified.

crab gender
Gender
weighing a crab
Weighing a crab

Weight and measurements

All crabs are measured and weighed.

measuring a carapace
Measuring a rab
needles disease
Pink crab

Microsporidian prevalence sampling

Needle condition

Needle condition - Nadelspora canceri is a microsporidian that infects the muscles of a crab, changing the meat to a white ‘cooked’ color while the crab is still alive. Some people notice a bad taste when eating an infected crab but consuming infected crab meat is not known to be harmful to humans.

Pink crab

Pink crab – A different type of microsporidian that infects the muscles of a crab can change the meat to a vibrant pink color while the crab is still alive. The pink crab infection rate is very low in Yaquina Bay (less than 1%) and again consuming pink infected crab meat is not known to be harmful to humans.

At the end of the day

All crabs are returned, unharmed, back into the bay at the end of the sampling day.

crab release

 

 Preliminary results

Dungeness crab abundance

In this figure, the total number of Dungeness crab that we capture in our research project varies depending on the season.  The numbers represent the average number of crab of all sizes that are found in each pot when they are pulled.  This a reflection of total abundance, which is greatest in the fall and least in the spring.  The number of crab per pull in Yaquina Bay and Alsea Bay is very similar to each other, and follows the same seasonal patterns.  Since the beginning of this research in May 2007, over 36,000 crab have been captured and measured in Yaquina and Alsea bays.

Number of crabs

Species composition

In Yaquina Bay, red rock crab and Pacific rock crab are captured along with Dungeness crab during our research sampling.  Dungeness are usually the most abundant crab captured in the pots, but in the spring red rock crab comprise a significant portion of the catch.  This is primarily due to the reduced abundance of Dungeness crab during the spring.  In Alsea Bay, our research sampling has never caught a red rock or Pacific rock crab, probably due to the lack of rocky habitat which rock crab prefer.
Proportion of Yaquina bay total catch by species

Sex ratio

The crab research conducted by ODFW has revealed that males and female Dungeness crabs are not caught in equal numbers. Overall, most of the Dungeness crab we catch are male, this is especially true in the winter. In the late summer-early fall, the male/female ratio is closer to 50/50. Possible reasons for these proportions varying throughout the season include the timing of various life history events, including molting, mating, egg extrusion, movements, etc.
Yaquina bay crab sex ratio from research pots

Legal sized Dungeness crab

Of particular interest to anyone wanting to catch Dungeness crab in Oregon’s bays is the best time of year to try bay crabbing. The ODFW crab research has found that in Yaquina and Alsea the best time to go bay crabbing is in the late summer through fall. This time of year has the greatest availability of male crabs over the legal size limit (5 3/4” across the back, NOT including the spines) because the annual summer molt has replenished the supply of legal-sized crab. Additionally, during this time male crabs from the ocean move into the bays. Male Dungeness crab in summer are typically soft because most have recently molted, but by the fall most of the legal-sized crab are firm and are filling out with meat.
number of legal Dungeness crab per pull

Research vs recreational catch

Coinciding with the crab research sampling, ODFW conducts a survey of recreational crabbers in Yaquina Bay and Alsea Bay.  The Catch per Unit Effort (CPUE) is a measure of success in the recreational fishery, often expressed as the average crabs per person interviewed during the survey.  The ODFW research success rates were standardized to make them comparable to the recreational fishery, and the results show that the recreational and research crabbing success rates follow the same seasonal pattern: more legal-sized male Dungeness crab are captured in the late summer and fall than any other time of the year.
Sport versus research catch

 

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