Spot Shrimp (Pandalus platyceros) Tag Study: streamer tag, PTMSC AmeriCorp
Kristin Wilkinson , PTMSC AmeriCorp 2006
2005 2006
Introduction: The Port Townsend Marine Science Center has partnered with the Washington Department of Fish and Wildlife to conduct a study on Spot shrimp (Pandalus platyceros). More than 80 shrimp species inhabit Washington waters, but little is known about each species. Shrimp are found primarily on or near the bottom, but make daily migrations through the water column in search of food. They have been found at depths greater than 1,000 feet, but are most frequently captured at depths of 30 to 300 feet. Adult shrimp are omnivorous, feeding on marine worms, small crustaceans, large planktonic organisms, spo
nges, and dead animal and plant material. In turn, a variety of fish prey on shrimp, including cod, lingcod, hake, flounder, halibut, dogfish, skates, and other bottom fish.
The family Pandalidae has a unique reproductive cycle, maturing first as males, then changing sex in later years to reproduce as females. Animals that display this characteristic are rare in nature and are know as Protrandous hermaphrodites.
Puget Sound shrimp spawn in late summer or fall, eggs develop in the female prior to spawning, and can be seen as a dark band just under the carapace. Shortly after mating, eggs are extruded and fertilized by a packet of sperm, called a spermatophore that was previously deposited by the male. Eggs are attached to the female’s specialized legs and are carried until they hatch in early spring.
Newly hatched shrimp larvae are small, about 5mm, planktonic and bear only a superficial resemblance to adult shrimp. About three months after hatching, larvae gradually start to take on the appearance and habits of adult shrimp. At this time the post-larvae settle in near-shore environments and mature as males within 18 months of hatching. At this time juvenile shrimp join the sub-adults/adults in distinct shrimp beds where they reproduce as males for one or two seasons before transforming into females. Females reproduce for one or two seasons, and research suggests they do not survive long after their final brood is hatched, typically after four or five years. The objective of this experiment to determine how long researchers can keep egg bearing females alive after spawning has taken place.
Methods: The Spot shrimp study began in February 2006 by tagging each individual shrimp with a Floy streamer tag (FTSL-73). The tag was inserted horizontally between the third and fourth abdominal plates as shown below.
The 29 shrimp used in this experiment were collected near Dungeness Spit in January of 2006 by biologists from the Jamestown S’Klallam tribe. The shrimp were caught at depths ranging from 250-300 feet and were ovigerous when delivered to the Port Townsend Marine Science Center. Each individual was measured for carapace length, observed for presence of eggs, egg condition, and any unusual physical features (black rot, disease, molting, or black gills.)
Results and Discussion: The first measurements were taken on February 28, 2006 and a total of 22 shrimp had eggs present. All data is entered into a spreadsheet detailing the date, tank number, tag number, length, condition of tag wound, egg presence and condition, and other comments. All data is attached to this report. Below is a sample of the data taken on February 28, 2006.
DATE |
TANK NUMBER |
TAG NUMBER |
LENGTH (mm) |
EGG PRESENCE AND CONDITION |
COMMENTS |
28-Feb |
Lab Tank L2 |
5 |
30 |
None |
|
28-Feb |
Lab Tank L2 |
36 |
39 |
Eyed |
|
28-Feb |
Lab Tank L2 |
37 |
40 |
Not Eyed |
|
28-Feb |
Lab Tank L2 |
38 |
38 |
Eyed |
|
Measurements were taken twice a month through April and once a month in May, June, July, and August. When measurements were taken April 7, 2006 it was observed that most of the eggs hatched and by April 21, 2006 all of the eggs hatched. Looking at the data very few females died after spawning, only 3 individuals died between April 21 st and May 18 th, 2006. Carapace length varies from start to end date, the average increase is 3.8 mm.
TAG NUMBER |
STARTING LENGTH 2/28/06 |
END LENGTH 08/09/06 |
5 |
30 |
36 |
36 |
39 |
40 |
39 |
39 |
41 |
44 |
33 |
38 |
45 |
36 |
41 |
46 |
39 |
44 |
47 |
37 |
40 |
49 |
38 |
42 |
51 |
36 |
40 |
54 |
37 |
41 |
56 |
37 |
40 |
57 |
39 |
41 |
59 |
38 |
42 |
60 |
32 |
37 |
61 |
35 |
39 |
62 |
29 |
34 |
64 |
31 |
35 |
65 |
32 |
36 |
One of the problems we encountered during the study was after several months the streamer tags would fall out or break. This caused problems because several shrimp do not have tags and data taken from that shrimp cannot be logged to an individual. Other issues came up when spawning occurred, since at the Port Townsend Marine Science Center we have open flow tanks we were unable to watch the development process and most of the offspring went through the pipes into the ocean.
Conclusion: Since the objective of this experiment was to determine how long researchers can keep egg bearing females alive after spawning has taken place and we still have females alive, we consider this experiment to be a success.
13 of the original ovigerous females spawned and are alive at the Port Townsend Marine Science Center as of August 9, 2006.