Long-Term Retention of Passive Integrated Transponder Tags Injected into the Pelvic Girdle of Adult Walleye

Many fish population studies rely on mark–recapture techniques to estimate important population statistics such as density, growth, recruitment, and mortality (Guy et al. 1996). Accurate estimates of population parameters are often limited by the ability to later detect marks or tags on individual fish. Hence, retention studies have been conducted for numerous tag/mark types applied at various fish anatomical locations since the 1940s in search of the “perfect mark” (Nielson 1992). Although the perfect mark may not exist, passive integrated transponder (PIT) tags implanted in fish muscle have had relatively high (> 90%) tag retention rates for a variety of fish species over 300 d (Harvey and Campbell 1989; Parker and Rankin 2003; Daugherty and Buckmeier 2009; Rude et al. 2011; Buckmeier and Reeves 2012). However, some studies also found that PIT-tag retention rates can vary according to species, size of fish tagged, tagging location, and tagging techniques used (Clugston 1996; Buzby and Deegan 1999; Kaemingk et al. 2011; Weber and Flammang 2017). Therefore, it is necessary to obtain species-specific estimates of long-term PIT-tag retention for the size range of fish tagged and desired injection location for mark–recapture models to be accurate (Miranda et al. 2002; Isermann and Knight 2005; Brenden et al. 2010).

One of the earliest long-term PIT-tag retention studies evaluated retention of PIT tags injected into the body cavity between the pelvic fins of Largemouth Bass Micropterus salmoides (Harvey and Campbell 1989). Although this technique had reported high retention rates, subsequent PIT-tag retention studies in salmonids found that PIT tags injected into the body cavity can enter the peritoneal cavity and create a potential problem with fish shedding tags during spawning (Prentice et al. 1990; Parker and Rankin 2003). Isermann and Carlson (2008) used a modification of this technique and injected 12-mm PIT tags via a 12-ga hypodermic needle posterior to the pelvic girdle of Black Crappie Pomoxis nigromaculatus to examine tag retention and to reduce the probability of the PIT tags being ingested by anglers. They found that short-term retention rates in this location were high (100%) and no PIT tags were found in fish fillets (81 tags in body cavity, 5 tags in muscle around pelvic girdle; Isermann and Carlson 2008). Vandergoot et al. (2012) injected PIT tags into the subcutaneous musculature between the pelvic fins of adult Walleye Sander vitreus as a secondary mark used in a multijurisdictional jaw tag retention study in Lake Erie and observed high PIT-tag retention rates for this location (98%). Walleye mark–recapture studies in Iowa have used visual implant tags injected in the clear tissue on the lower mandible, but recent estimates of tag retention in this location have been less than desirable (i.e., 76–80%; Meerbeek et al. 2013; Meerbeek 2017). Implanting PIT tags in the dorsal musculature of Walleye has resulted in high tag retention rates (99.5%; Weber and Flammang 2017), but since Walleye are a major sport fish targeted for consumption, managers wanted to avoid this location for marking to reduce angler–PIT-tag interactions. Therefore, an alternative PIT-tagging location was needed for adult Walleye. The objective of this study was to evaluate long-term retention rates of PIT tags injected into the musculature between the pelvic girdle of adult Walleye.

We collected Walleye from a chain of lakes in northwestern Iowa during April 2015 via short-term (2-h) gill-net sets, transported them to a state fish hatchery, and held them in cement raceways using the same procedures as described in Meerbeek et al. (2013) and Meerbeek (2017). After hatchery staff processed Walleye, they placed male and female Walleye in separate raceways and then measured (total length [TL]; nearest 2.54 mm) each fish and checked for an existing visual implant alphanumeric (VIA) tag. We selected only previously VIA-tagged (single or double VIA; see Meerbeek 2017) adult Walleye as study fish since tag shedding rates of VIA tags that have been implanted ≥ 1 y are extremely low (< 5%; J. Meerbeek, unpublished data). Once we encountered a previously VIA-tagged Walleye, we recorded the VIA tag information and inserted a 12-ga hypodermic needle loaded with a 12-mm PIT tag (HPT12; 134.2 kHz; Biomark, Inc., Boise, Idaho) just anterior to the pelvic girdle (needle pointed toward head; Figure 1), with the tag being implanted within the intraperitoneal space or pelvic musculature. After tagging, we used a Biomark model 601 handheld radio-frequency identification tag reader to ensure the PIT tag functioned properly and then transfer the PIT tag data into an electronic database. The same individual performed all tagging in April 2015; then we released all PIT-tagged Walleye back to the lake of capture. We recaptured Walleye during annual gill-netting surveys conducted from March to April 2016–2019 (see Meerbeek et al. 2013 and Meerbeek 2017). We scanned recaptured Walleye each year using the handheld tag reader to check for a PIT tag. If we detected no tag, workers examined the fish for a VIA tag. If VIA tag information corresponded to a fish that had been PIT tagged in 2015, the fish was determined to have lost the PIT tag. We recorded all other tag information, and measured and released the Walleye.

We implanted a total of 115 female Walleye (range = 485–706 mm; mean TL = 572 mm; standard deviation [SD] = 50) and 217 male Walleye (range = 444–645 mm; mean TL = 529 mm; SD = 31) with PIT tags in 2015 (Data S1, Supplemental Material). We recaptured 88 Walleye (72 males and 16 females) up to 4 y after tagging (359–1,476 d; Data S2, Supplemental Material). Of the 57 fish captured between 359 and 376 d after tagging, one fish (589-mm female) lost the PIT tag. None of the remaining 31 Walleye captured up to 1,476 d after tagging had lost the PIT tag. Collectively, 87 of the 88 (98.9%) recaptured Walleye retained the PIT tag up to 4 y after tagging. These results were very similar to those observed by Vandergoot et al. (2012; 98%) for similar-sized Walleye (mean TL = 508 mm; range = 318–818 mm) PIT tagged in the isthmus and recaptured up to 3 y after tagging in Lake Erie. There was no evidence to suggest that PIT tags injected in this location are prone to tag shedding upon future recaptures as we captured 23 Walleye in this study more than once and all Walleye had retained their tag on their second or third recapture. Others have suggested that most PIT-tag loss occurs within the first few days after tagging (Dare 2003; Wagner et al. 2007). This study was limited to annual recaptures of fish; however, we recaptured three fish via gill nets shortly after we PIT tagged (<1 wk after tagging) and released them back into the lake and all of these fish retained their tag.

Few studies have evaluated PIT-tag retention in adult Walleye (see review by Musselman et al. 2017), yet Walleye population dynamics and harvest statistics are often sought by many jurisdictions within North America (Baccante and Colby 1996). Estimates of these parameters in some cases have been severely under- or overestimated using conventional tag types (e.g., jaw, visual implant, anchor) because of poor long-term retention rates (Isermann and Knight 2005; Koenigs et al. 2013; Meerbeek et al. 2013). The data presented here and by Vandergoot et al. (2012) demonstrate that the pelvic girdle is an effective PIT-tagging location for long-term studies evaluating adult Walleye population dynamics. In addition to having high tag retention rates, the placement of the tag within the pelvic girdle drastically reduces the probability of tags being found in fish fillets (Parker and Rankin 2003; Isermann and Carlson 2008) and offers a suitable location for Walleye that are often targeted for consumption in Iowa and elsewhere (Gaeta et al. 2013). Furthermore, Dembkowski et al. (2018) found high retention and low mortality rates for small Walleye (93–216 mm) injected with 12-mm PIT tags in the pelvic girdle. Although their study only evaluated short-term (7-d) retention of PIT tags for small Walleye, the ease of tag insertion and low mortality rates (< 5%) they reported at low water temperatures (< 17°C) provides managers with alternative tagging locations that may improve stocking assessment evaluations, reduce PIT-tag–angler interactions, and maintain consistency among PIT-tagging location among all sizes of Walleye. These studies collectively demonstrate that PIT tags inserted into the pelvic girdle of a range of Walleye sizes yield retention rates suitable for advanced population modeling or stocking evaluations.

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Data S1. Tag and fish-length data for male and female Walleye Sander vitreus collected from natural lakes in Iowa in 2015 and injected with passive integrated transponder tags in the pelvic girdle.

Found at DOI: https://doi.org/10.3996/JFWM-20-015.S1 (33 KB XLSX).

Data S2. Date of recapture and length data for male and female Walleye Sander vitreus injected with passive integrated transponder tags in the pelvic girdle and recaptured up to 4 y after tagging in natural lakes in Iowa.

Found at DOI: https://doi.org/10.3996/JFWM-20-015.S2 (22 KB XLSX).

This research was funded in part by the Federal Aid in Sport Fish Restoration program. D.J. Vogeler, Jim Berquist, and the crew at the Spirit Lake Fish Hatchery assisted with fish and data collection.

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