Spot Shrimp (Pandalus platyceros) Tag Study: a comparison of three tag types, streamer tag, Floy anchor T-bar tag and a telson clip
Laura Friedenberg, PTMSC AmeriCorp 2005 and Kathryn Kegel, Fall Intern 20052005 2006
Introduction
More then eighty shrimp species inhabit Washington waters. Seven of these species are economically important and belong to the family Pandalidae. They share a similar life history and have 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 subadults/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.
Recent studies also suggest that increased fishing pressure or high natural mortality can induce males to change into females at a younger age, or completely skip the make phase. A few individuals will skip the male phase and spend their entire lives as females. This reproductive strategy may help to ensure that there is an adequate supply of egg-producing females each year.
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 thatn 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, and dead animals 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 objective of this investigation is to examine external tag types and make recommendations as to which tag type(s) may be appropriate for mass marking by shrimp researchers and WDFW staff during future investigations. This study will examine the effect of tag types on growth, mortality and to some extent behavior on Spot shrimp (). This investigation will also help to provide a basis in which future-tagging projects will be implemented so that the life history of the Spot shrimp can be better understood. Currently, due to a paucity of research, little is known about the life history of P. platyceros in Puget Sound.
Methods
Three different tag types will be examined and compared, including a Floy streamer tag (FTSL-73), Floy anchor T-bar tag (FD-68B), and a caudal (telson) clip. A total of 20-30 shrimp of various sized will be used for each tag type. A control group of equal size will be included. Therefore, approximately 80-120 shrimp will be collected and kept at the Marine Science Center Discovery Lab. Tag types were mixed together and equally divided into at least three replicated, that is, shrimps were kept in three different tanks and aquaria. Salinity and water temperature were kept at similar levels for each treatment. Shrimp were kept under normal photoperiods.
Tag placement
The two external tags were attached to the shrimp following methods utilized in previous investigations. Application of the streamer tag followed methodologies described by Kimker et. Al. (1984) and Jewett (1986) for spot shrimp (P. platyceros). In these studies the streamer tag was attached by pulling it through the abdomen between the first and second abdominal plate with a sterilized needle (Figure 1).
Figure 1. Floy streamer tag placement
The Floy anchor tag was applied to the shrimp utilizing a protocol described by Schwartz (1977) in his investigation on white shrimp (Penaeus setiferus). In this work the tag was inserted in a horizontally perpendicular fashion between the third an fourth abdominal plates (Figure 2).
Figure 2. Floy anchor tag placement
The telson (there are two, one on each side of the uropod) clips were used to examine regeneration of the uropod (tail). A small piece of the telson was clipped off in a diagonal direction (Figure 3). Clips of this nature are commonly used to mark animals and could be used in mass marking tag programs.
Figure 3. Location of Telson clip
Tagged animals were examined for growth, tag retention, infections, wounds, molting, ovigery and behavioral changes on routine basis. Initial measurements of the shrimp’s carapace were taken and re-measured on a monthly basis. After each shrimp died, final observations were made and recorded including carapace measurement, sex, and wound condition.
Results and Discussion
Table 1: Average number of days survived and carapace growth for each of the three different tags types as well as the controls.
Tag Type |
Control |
Streamer |
Anchor |
Telson |
Average number of days survived (days) |
141 |
82 |
76 |
105 |
Average Carapace growth (cm) |
1.39 |
0 |
0.78 |
2.10 |