Tag Shedding Research Articles

Mortality estimates for juvenile dusky sharks Carcharhinus obscurus in South Africa using mark-recapture data

A maximum likelihood model is developed, using mark-recapture data, to estimate total and fishing mortality rates for the dusky shark Carcharhinus obscurus in South Africa. The model accounts for tag-shedding, nonreporting of recaptured tags, the multiple release and single recapture nature of the study and the usage of two different types of tags (sheep-ear and ORI tags). Tag shedding was quantified as tags washed up on beaches and fouling of tags in protective shark nets, which amounted to 17% of all tags recovered between 1986 and 1993. The ORI tag had a higher tag-shedding rate than the sheep-ear tag. Assuming a 75% reporting rate for recaptured dusky sharks, an instantaneous fishing mortality rate was estimated to be 0.27.year–1, with a 95% confidence level ranging between 0.19 and 0.44.year–1.

Mortality and tag loss in dart and loop‐tagged captive snapper, Pagrus auratus (Sparidae), with comparisons to relative recapture rates from a field study

Tag shedding rates of Hallprint dart and loop tags, and tag‐related mortality in the snapper Pagrus auratus were experimentally determined on fish held in captivity for periods up to 18 months. An artefact of the experimental process appeared to exacerbate dart tag shedding in one treatment. However, for other treatments, the instantaneous shedding rates for the first 7 months was 0.0006 day−1. Shedding rates were not linear for periods beyond 7 months and were described by a logistic function. The instantaneous shedding rate for the loop tags was much lower at 0.00016 day−1. Overall mortality during the experiment was only 1.9% and the causes of death could not be related to tagging. The relative return rates of the two different tag‐types from a field tagging programme were compared after analysis of fish size, spatial, temporal, and tagger‐type distribution. In all direct comparisons within each stratum, loop tag return rates were higher. It was concluded that the retention capabilities are better for loop tags than for dart tags in P. auratus.

Tagging eastern rock lobsters Jasus verreauxi: effectiveness of several types of tag

An experiment was done in the laboratory over 147 weeks to assess tag loss (tag-induced mortality plus tag shedding) in tagged or marked eastern rock lobsters, Jasus verreauxi. The incidence of tag-induced mortality, tag shedding or tag loss did not generally differ among tag types (toggle, T-anchor, dart tags), mark, or untagged lobsters. The exceptions were that more untagged lobsters died between weeks 86 and 147 than lobsters tagged with T-anchor or dart tags. The percentages of lobsters that died were 51, 45, 43, 47, and 62 for toggle, T-anchor, dart, marked, and untagged treatments, respectively. An additional 18%, 22% and 23% of lobsters tagged with either toggle, T-anchor or dart tags, respectively, shed their tag. None of the marked lobsters lost their marks. We conclude that no one type of tag used in the experiment was more suited to tagging J. verreauxi than another. Marking was discounted as a technique to use in long-term experiments because, although the mark was still evident after 147 weeks, only trained observers could recognise it, making the technique inappropriate for the general public.

Comparison of Three Nonlinear Models to Describe Long-Term Tag Shedding by Lake Trout

Abstract We estimated long-term tag-shedding rates for lake trout Salvelinus namaycush using two existing models and a model we developed to account for the observed permanence of some tags. Because tag design changed over the course of the study, we examined tag-shedding rates for three types of numbered anchor tags (Floy tags FD-67, FD-67C, and FD-68BC) and an unprinted anchor tag (FD-67F). Lake trout from the Gull Island Shoal region, Lake Superior, were double-tagged, and subsequent recaptures were monitored in annual surveys conducted from 1974 to 1992. We modeled tag-shedding rates, using time at liberty and probabilities of tag shedding estimated from fish released in 1974 and 1978–1983 and later recaptured. Long-term shedding of numbered anchor tags in lake trout was best described by a nonlinear model with two parameters: an instantaneous tag-shedding rate and a constant representing the proportion of tags that were never shed. Although our estimates of annual shedding rates varied with tag type ...

Sphyrion Tag Shedding and Tag Induced Mortality of the American Lobster, Homarus Americanus H. Milne Edwards, 1837 (Decapoda, Nephropidae)

Sphyrion tags are commonly used for studying movement and growth of the American lobster, Homarus americanus. Observations in the laboratory suggested that shedding of sphyrion tags and tag induced mortality occurred mainly within the first 5 days after tagging or during molting, depending upon the molt stage of the lobster at tagging. Shedding rate varied from 3.1 % (within 5 days after tagging) for individuals tagged at the early prcmolt stage to 21.7% (during molting) for those tagged at the late prcmolt stage. Tag induced mortality varied from 3.1 % (within 5 days after tagging) for individuals tagged at the early premolt stage to 23.3% (within 5 days after tagging) for those tagged at the postmolt stage. Shedding of tags and tag induced mortality were significantly high for lobsters tagged at the late premolt and postmolt stages, respectively. Therefore, it is preferable that lobsters be tagged during the intermolt period to minimize shedding of sphyrion tags and tag induced mortality. A tag-recapture study in the field showed that the recapture rate of lobsters tagged with streamer tags was significantly higher (43.8%) than that for those tagged with sphyrion tags (19.2%). This suggests that tag loss among lobsters tagged with streamer tags may be less than that among lobsters tagged with sphyrion tags.

Sphyrion Tag Shedding and Tag Induced Mortality of the American Lobster, Homarus Americanus H. Milne Edwards, 1837 (Decapoda, Nephropidae)

Sphyrion Tag Shedding and Tag Induced Mortality of the American Lobster, Homarus Americanus H. Milne Edwards, 1837 (Decapoda, Nephropidae)

Growth, Movement, Recapture Rate and Survival of Hatchery-Reared Lobsters (Homarus Gammarus (Linnaeus, 1758)) Released Into the Wild On the English East Coast

From 1983 to 1988 over 49,000 three-month-old hatchery-reared lobsters were tagged with a microwire tag and released into the wild in Bridlington Bay on the east coast of England. The area supports a substantial fishery based on a large stock of naturally settled lobsters. Since 1988 approximately 57,000 lobsters have been tested at sea and at the landing place in order to recapture microtagged lobsters and assess their growth, movement, recapture rate and survival. Results to date show that microtagged lobsters have survived in the wild for up to eight years and have been caught in traps (or pots) by commercial fishermen. Lobsters began to reach the minimum legal size of 85 mm carapace length four to five years after release, but showed substantial individual variation in size at age. Most recaptures were recorded within six kilometres of known release sites, and showed strong site fidelity. Some recaptured females carried eggs. Data from additional T-bar tag-recapture experiments are used to estimate the exploitation rate generated by standard pots assuming either zero or a high rate of T-bar tag mortality and tag shedding. The exploitation rate is used to convert spot estimates of the catch rate of microtagged lobsters into estimates of their abundance for comparison with the number of lobsters released at individual sites. Corresponding estimates of survival from release to recapture average 84% and 50% for the two assumptions made about tag mortality and tag shedding in the T-bar tag-recapture experiment. It appears that juvenile hatchery-reared lobsters have survived well to recruitment and we offer this as a first quantitative assessment of pre-recruit survival for Homarus gammarus. The significance of this result for lobster stock enhancement and ecology is discussed.

A new technique for tagging abalone

A new technique for individually marking abalone in situ uses a nylon rivet to attach a numbered disc to the trema. In trials with Haliotis rubra, there was an initial loss of 4-16% and an annual rate of tag shedding of approximately 4-35%. Rates of tag loss depended on the positioning of the tag. The ease with which this technique can be used under water, the speed of application, and the low level of irritation expected to result from its use make this a useful addition to the range of techniques available for the study of abalone.

Determination of Fish Movement Patterns from Tag Recoveries using Maximum Likelihood Estimators

A general method for analysis of movement data from tag returns is proposed which has four major components: (1) a population dynamics and movement model that describes how the number of tagged individuals in each spatial location changes over time; (2) an observation model which describes how the tags are recovered and reported; (3) a likelihood function that specifies the likelihood of observing a specific number of recoveries in each space/time stratum as a function of the number thought to be there under a specific set of parameters of the population dynamics, movement and observation models, and (4) a nonlinear function minimization computer algorithm. This approach is applied to movements of skipjack tuna (Euthynnus pelamis). When tagging and recapture take place in each spatial stratum, reliable estimates of movement rates can be obtained. The approach described is completely general and can be used in cases where movement takes place continuously, or only once in the life history. Methods for determining confidence limits and evaluation of residuals are presented and extensions that include tagging mortality, tag shedding, and size specific vulnerability are discussed.

Tag loss and mortality rates of a small tropical demersal fish species, Lutjanus carponotatus (Pisces : Lutjanidae), tagged with dart and anchor tags

The shedding rate of FD-67 anchor tags from L. carponotatus was significantly lower than that of FT-2 dart tags. Mortality in fish tagged with either the FT-2 dart or the FD-67 anchor tags was significantly higher than in the untagged controls. There was no significant difference between mortalities caused by the two types of tag. Combining tag shedding and tag-induced mortality, the FT-2 dart tag produced a significantly greater rate of disappearance of tagged fish from a tagged population. Tag-induced mortality was highest during the first week after tagging and greatly reduced thereafter.

Selection of External Tags for Marking Atlantic Herring (Clupea harengus harengus)

Of seven external tags (carlin, disc and disc, disc and dangler, anchor, short anchor, dart, streamer) applied to Atlantic herring (Clupea harengus harengus), the anchor tag is the best to use when tagging rate, recovery rate, and persistence of tagged fish in the population are considered. A high recovery rate for carlin tags was more than compensated by the higher application rate exhibited by anchor and dart tags. Anchor tagged fish had a lower sustained mortality and reduced time in setting up the tags for application compared to dart tags. Tagged herring suffered higher short and apparent long-term mortalities than the unmarked population regardless of which external tag type was applied. Long-term tag loss may have been due to tag induced mortality and/or tag shedding. Consequently, studies requiring data beyond 2 yr after release would need another type of tag. Initial mortalities of herring increased with holding and handling time for all tags tested. This result confirms that herring should be tagged immediately after capture to reduce initial mortalities.

Migration model and dynamics parameters of large-sized yellowtails in the Pacific along the Japanese coast inferred from tag recaptures after the year of release.

1. A system model on fishing, migration and survival of the tagged yellowtails after the year of release was developed. The data of tag recaptures after the year of releases of the large-sized fish tagged in 1926 to 1938 period were applied to the model and the rate of disappearance from fishing ground, proportion of fish reappearing next year first to each fishing ground, and natural mortality rate were estimated. Some of these values were compared with the estimates from the same year recaptures. 2. The rate of disapearance during the fishing season was high in Kumano-nada and Tosa Bay likewise the results from the same year recaptures. Discontinuity in the distribution of fish at these points was reaffirmed. Majority of the fish released in Sagami Bay and Kumano-nada reap-peared first to Kumano-nada next year, while the fish released in Kyushu area returned to the same area. Estimates of the natural mortality rate. between fishing seasons ranged from 57% to 70 (M=0.84-1.20) and the weighted mean was 61% (M=0.94). If such factors as tag shedding and tag martality were affecting, these values would be overestimation. For the fish released in Sagami Bay and Kumano-nada, no southward shift of areas of recapture was observed according to the number of years after release. Estimates from the recaptures in second year and in and after third year showed similar values. 3. The fishing rates for the tagged fish after the year of release and some of the rates of disappearance were assumed to be the same as that in the year of release. Even if this was not the case, effect on estimation error of the rate of disappearance would be small. It is possible that the bias of overestimation of the survival rate is as large as 50% but actually such a large bias seems to be unlikely.

Generalized models for the estimation of rates of tag shedding by southern bluefin tuna (Thunnus maccoyii)

Generalized models for the estimation of rates of tag shedding by southern bluefin tuna (Thunnus maccoyii)

流れ藻の標識放流によりモジャコ漁獲率を推定する場合の数学的モデルについての若干の検討

The basic model for the number of tags N presented in the previous paper is modified, in order to take into account the fact that tags shed from seaweeds are not vulnerable to the fishery, and hence the coefficient of fishing κF can be applied only to retained tags NT, but not to the total tags N. The results from a modified model are compared with those from the previous one. It reveals that the results from the latter, which is very simple in expression, is a good approximation to that from the former and the error involved in the estimate of the coefficient of tag shedding M based on the previous model is thought to be negligible. This modification of the model does not affect the estimates of other parameters such as κF.

流れ藻標識脱落係数の推定

1) A trial for estimating the tag shedding rate from drifting seaweed was made. This was needed to evaluate the rate of exploitation of drifting seaweeds from the tagging experiments of them. 2) The maximum likelihood estimates were obtained for three groups in different years and/or areas of release by means of iteration. The precision of the estimates were also evaluated. 3) The values of the coefficient of tag shedding ranged 0.017-0.022 with the average of 0.019 which is close to 2% per day. The difference between years or areas of release was not demonstrated. The coefficients of variation of the estimates were roughly within the range of 20-30%.