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Evidence of predation of juvenile white sturgeon (Acipenser transmontanus) by North American river otter (Lontra canadensis) in the Nechako River, British Columbia, Canada

J Appl Ichthyol. 2020;00:1–5.
  1© 2020 Wiley-VCH GmbH
Received: 19 March 2020 
  Revised: 3 Se ptembe r 2020 
  Accepted: 11 Sep tember 2020
DOI : 10.1111/jai.14114
Evidence of predation of juvenile white sturgeon (Acipenser
transmontanus) by North American river otter (Lontra
canadensis) in the Nechako River, British Columbia, Canada
C. N. Babey1| N. Gantner1,2 | C. J. Williamson3| I. E. Spendlow2|
J.M. Shrimpton1
1Faculty of Environment, University of Northern British Columbia, Pr ince George, Br itish Columbia , Cana da
2BC Ministry of Forests, Lands, Natural Resource Operations and Rur al Development, Prin ce George, Brit ish Colu mbia, C anada
3Nechako W hite Stur geon Recovery Initiati ve, Vanderhoof, Bri tish Col umbia, Canad a
Correspondence: Cale Bab ey, Faculty of Environment, University of Northern British Columbia, Pr ince George, Br itish Co lumbia , Cana da.
Funding information
Fisheries and Oceans Canada; Un iversi ty of Nor thern British C olumbia; BC Minis try of Forest s, Lands, Natural Resource Operations & Rural Develo pment;
Natural Sciences and Engineering Research Cou ncil of Canada
Keywords: otter, PIT tag, predation, radio tag, white sturgeon
White sturgeon (Acipenser transmontanus) in the Nechako River,
British Columbia, Canada have experienced recruitment failure since
1967 (Mc Adam et al., 2005) and this population was listed as en-
dangered under the Species at Risk Ac t (SAR A) in 2006 (Fisheries
& Oceans Canada, 2014). A conservation aquaculture facility, the
Nechako White Sturgeon Conservation Center (NWSCC), began re-
leasing cultured juvenile Nechako white sturgeon into the Nechako
River in 2015 (Hildebrand et al., 2016). All sturgeon released from
the NWSCC have been implanted with a passive integrated tran-
sponder (PIT) tag to identify hatchery-reared fish, but also track
growth and movement for fish captured post-release (Gibbons &
Andrews, 2004). Tags that withstand predation events are a useful
tool to study sources of predation when retrieved from defec ation
sites (Evans et al., 2012; Gibbons & Andrews, 2004). Of the released
sturgeon, a proportion have additionally been implanted with a radio
tag to track movement, habitat use, and sur vival. Radio tags can also
be detected out of water and the locations of tags on shore may
indicate feeding sites of semiaquatic predators.
Radio telemetry surveys indicated that many hatchery-released
juvenile Nechako white sturgeon lacked observable movement and
tags were detected on land suggesting interac tions with a semi-
aquatic predator. In central British Columbia, the Nor th American
river otter (Lontra canadensis) is one potential piscivorous predator
large enough to prey on hatchery-released white sturgeon. Our ob-
jective was to identify a previously unstudied interaction between
juvenile Nechako white sturgeon and the North American river
otter. Sturgeon radio tags were collected in suspected otter feeding
sites and sturgeon PIT tags were collected from otter latrine sites.
We recommend further research to determine the impact this pre-
dation has on the success of the conservation aquaculture program
for the Nechako white sturgeon.
The Nechako River is located in central British Columbia and runs
for approximately 280 km until flowing into the Upper Fraser River
in Prince George, BC. It has been regulated upstream by the Kenney
Dam since 1952, with white sturgeon present below the dam. To
compensate for the decline in population size, white sturgeon have
been released from the NWSCC in April or May of each year with
an additional fall release in 2018 (Table 1). All released fish were
PIT tagged (FDX-A 12 mm tags; Biomark, Boise, ID) with a portion
also fitted with radio tags (model MCFT2-3BM or MCFT2-3L; Lotek,
Newmarket, ON). Radio tag weight ranged from 1% (2019) to 3.6%
(2017) of fish body weight out of water and fish were monitored
   BABEY Et Al.
in the hatcher y for at least 3 weeks prior to release. Using a Lotek
SRX800 radio receiver, seven to fourteen boat-based sur veys were
conducted to track movements of released fish bet ween April and
November annually from 2015 to 2019; survey dates varied across
years. An additional one to seven helicopter-based surveys were
conducted annually using a Lotek SRX600 radio receiver and direc-
tional antenna (model R2-AHS; Telonics Inc., Mesa, AZ). Tags that
lacked observable movement over multiple boat and helicopter
surveys were then tracked to shore during boat surveys, and where
possible collected using a Lotek SRX8 00 radio receiver.
From 2016 to 2018, collection of PIT tags was initially conducted
opportunistically by searching the bank of the river near the loca-
tions of collected radio tags and by looking for river otter scat or
other indicators of latrine sites. River otters establish latrine sites
for scent based communication with other otters (Depue & Ben-
David, 2010), but deposited scat also contains indigestible parts of
their meal, such as the PIT tags from sturgeon prey. In addition to
opportunistic searches, in 2019 we targeted river features that la-
trine sites are commonly associated with such as deep pools, beaver
(Castor canadensis) lodges, and mouths of tributary streams (Depue
& Ben-David, 2010; Swimley et al., 1998). Sturgeon were released
into the Nechako River between river kilometers (RKM) 117 and 197.
Latrine site searches and PIT tag collections reported in the pres-
ent study occurred near the town of Vanderhoof, BC (54.0140°N,
124.0130°W) between RKM 105 and 140. One site was discov-
ered oppor tunistically near RKM 200 during an exploratory search
to collect radio tags lacking observable movement. On shore, PIT
tags were detected using a Power Tracker V PIT tag reader (Avid
Identification Systems Inc., Norco, CA). After the detection of a tag,
readers with a smaller search radius (Biomark HPR Lite and Biomark
Gl ob al Po ck et Read er Plus) we re used to lo c at e tag s. Co des of re cov-
ered tags were entered into the NWSRI (Nechako White Sturgeon
Recovery Initiative) database to obtain information for each individ-
ual fish such as release date, release location, size at release, and
post-release capture information.
In 2016, 16 radio tags were physically recovered near-shore or on
land. An additional seve n tags could not be retr ieved, but we re id en-
tified to be mortalities due to their location and absence of observ-
able movement. The collections in 2016 provided the first evidence
of predation. Of the 137 radio-tagged sturgeon released since 2015,
71 have been confirmed as mortalities to date (Table 1). Of these, 36
tags have been physically recovered, while 35 tags have not been
recovered, but were confirmed to be mortalities. Unrecovered tags
were typically difficult to retrieve due to being buried in thick brush,
beaver lodges, or in the substrate under water close to shore. In July
of 2019, a par tial carcass of the second largest confirmed mor talit y
(fork length 69.8 cm and mass 2.12 kg at release) was found sur-
rounded by otter prints at a site approximately 10 m upstream of
an otter den and about 30 m away from an identified latrine site
TABLE 1 Summary of white sturgeon released with passive integrated transponder (PIT) tags, radio tags, and the number of tags recovered along the Nechako River. Number of tags are
presented by release year and tag type. The range of size at release (fork length in cm) for confirmed mor talities of white sturgeon is shown by tag type and mean lengths of all releases shown
for comparison
Release year
Fish released with
radio tags
Confirmed radio tagged
fish mor talities (%)
Size at release for fish with radio tags
recovered (mean ± 1SD of all radio t ag
releases) (cm)
Fish released
with PIT tags
PIT tags
recovered (%)
Size at release for fish with PIT tags
recovered (mean ± 1SD of all PIT tag
releases) (cm)
2015 30 9 (30) 45.5–50.2 (39.7 ± 8.65) 1,247 8 (0.64) 29.7–43.8 (41.7 ± 4.7)
2016 30 23 (76.7) 30.1–49.9 (32.9 ± 1.7) 9,162 121 (1.32) 20. 5–40.9 (33.7 ± 4.1)
2017 15 14 (93.3) 30.9–36.8 (39.7 ± 8.3) 11,488 185 (1.61) 23–37.8 (30.6 ± 2.4)
2018 spring 32 21 (65.6) 50.8–59.8 (55.0 ± 2.9) 4,354 103 (2.37) 25.8–55.4 (29.6 ± 3.1)
2018 fall 0NA NA 3,558 64 (1.80) 16.0–31.2 (25.2 ± 3 .9)
2019 30 4 (13.3) 62.9–70.8 (69.0 ± 6.1) 606 42 (6.93) 24.2–41.8 (38.9 ± 10.8)
Tot a l 137 71 (51.8) 30.1–70.8 (48 .9 ± 14.3) 30,415 524 (1.72)a 16.0–55.4 (31.5 ± 5.5)
aRelease year for one of the tags is unknown due to the tag being broken and its code unreadable.
(Figure 1a). This was the only tag found to date where parts of the
associated carcass remained during tag collection.
Following the first retrieval of radio tags in the fall of 2016, a
single latrine site was identified in the vicinity of two recovered radio
tags. A search of this site resulted in the first 10 PIT tags retrieved,
providing a second line of evidence of otter predation. Since this first
discovery, an additional 26 latrine sites have been identified and a
total of 513 PIT tags retrieved from the 27 sites (Figure 2; Table 2).
The increase in PIT tag collections in recent years is attributed to
increased effort to identify latrine sites. Latrine sites were revisited
and additional tags recovered from scat, including fresh scat indi-
cating recent predation (Figure 1b). In addition to recoveries from
latrine sites, eleven PIT tags were collected from seven suspected
otter feeding sites. The number of PIT tags retrieved from each la-
trine site ranged from 0 to 87, collected during a minimum of two
visits. The proportion of PIT tags recovered from a particular release
FIGURE 1 (a) Partial carcass of a
radio-tagged juvenile white sturgeon
released from the Nechako White
Sturgeon Conservation Centre. The fish
was 69.8 cm (fork length) and 2.12 kg at
release 28 days before the carcass and
tag were discovered. (b) Three passive
integrated transponder (PIT) tags found
in a single otter scat . All three tags were
from hatchery-released white sturgeon
FIGURE 2 Map of primar y study area showing identified latrine sites and the number of hatchery white sturgeon PIT tags collected
from each site. River kilometers (RKM's) and the town of Vanderhoof, BC are shown for reference. Insert map of Canada shows approximate
location of study area in British Columbia
   BABEY Et Al.
year ranged from 0.64% (2015) to 6.93% (2019), with a total pro-
portion across all release years of 1.72% (Table 1). Five PIT tags
retrieved from latrine sites matched radio tags from st urgeon identi-
fied as mortalities. The distance between the recovered PIT tag and
radio tag for these five fish ranged from 200 m to 2.7 km; PIT tags
were found upstream of the radio tags for one and downstream for
four of the mortalities. Five PIT tags were recovered that belonged
to juvenile sturgeon that had at least one post-release capture event,
with one having two captures prior to predation. A single PIT tag
belonging to a wild juvenile white sturgeon was recovered from a
latrine site in 2020, providing evidence of otter predation of wild
individuals in the Nechako River. Based on capture history, this stur-
geon would have been at least 19 years old and 69 cm fork length.
We prov ide evidence of a previously unstudied pred ation of juvenil e
Nechako white sturgeon by river otters through the collection of up
to 36 hatcher y-raised juvenile white sturgeon radio tags from sus-
pected otter feeding sites and 513 PIT tags from otter latrine sites.
The identification of a source of mortality is important in evaluating
the succes s of the co nser vation aqua culture program fo r th is endan-
gered population. This predation was suspected when one juvenile
sturgeon radio tag and one acoustic tag were tracked to a beaver
lodge after a pilot hatcher y release in 2007–2008. Collec tion of
radio tags from shore after telemetry surveys showed they lacked
observable movement in 2015 and provided evidence of river otter
predation. Several tags had chew marks at the base of the antenna
suggesting it was a predator with teeth that chews its prey after
bringing the prey to shore; a common behaviour of river otter if fish
ar e too bi g to ha ndl e in the wa te r (Kr uuk , 200 6). Th e loc ation s of se v-
eral retrieved tags also had the presence of freshwater mussel shells,
a documented food source for river otters (Crowley et al., 2013;
Serfass et al., 1990). Many tags were found in areas with extensive
cover such as under bushes, trees, or tall grass. LeBlanc et al. (2007)
documented the importance of vegetation cover for otters when
they are associated with beaver ponds and suggested protection
from terrestrial predators as a possible explanation. Additionally,
some t ags were found in or near beaver lodges, which are common
areas for river otter feeding and activity (Reid et al., 1994).
Predation by river otters was confirmed through the collection of
PIT tag s from riv er ott er latrine site s. Sever al tag s we re found in eas-
ily identifiable otter scat, or mixed with the hard parts of fish, which
is indicative of decomposed otter scat (Kruuk, 2006). It is difficult to
be confident that all radio-tagged sturgeon mor talities are a result of
river otter predation, however there is evidence that at least a pro-
portion of radio-tag mortalities were caused by otters. The collec-
tion of five PIT tags in latrine sites that belonged to fish whose radio
tags were also found provides the strongest evidence that at least
a propor tion of radio tag mortalities are a result of ot ter predation.
Given the relatively large size of the radio tags, they are unlikely
to be ingested by the otter and therefore their locations are more
TABLE 2 PIT tag retrievals by year collected, number of latrine sites identified, frequency of visits, feeding sites identified, and amount of shoreline sur veyed to identify latrines in each
PIT tag collection year
No. of latrine sites found
(frequency of visits)
No. of PIT tags recovered from
latrine sites
No. of PIT tags recovered from suspected feeding
sites (no. of sites)
Length of shoreline intensively sampled
to identif y latrines (km)
2016 1 (1) 10 0 0
2017 1 (1) 16 0 0
2018 5 (1) 92 1 (1) 0
2019 20 (2–4) 395 10 (6) 12
Tot a l 27 513 11 (7)
indicative of feeding sites while PIT t ags are much smaller and more
likely to be ingested by the otter and defecated in a latrine site.
The 11 PIT tags found in sites with characteristics of feeding sites
may indicate that some PIT tags are not ingested during a feeding
event. Large-scale factors limiting detection of all PIT tags include
the ability to identify all latrine sites and not all PIT tags ending up
in latrine sites; while site-level detection is limited by short detec-
tion range, tag collision, broken tags, and tags being washed down-
stream. Alternatively, the long-range detection ability of radio tags
allows most of them to be accounted for and may explain the much
larger proportion of radio t ags retrieved. There is currently insuf fi-
cient data to suggest a tagging effect resulting in higher predation
vulnerability of radio tagged sturgeon. Even with this uncertainty,
the collection of both tag types provides evidence of clear predation
by North American river ot ter.
Recent evidence of predation on a wild juvenile white sturgeon
raises concern about the potential impact of this predation of wild
individuals. Although we present our findings as an unstudied inter-
action, it is not an unexpected one given that both are native species,
but also the importance of fish to otter diet. We acknowledge the
limitations of our current findings for determining the extent of this
predation and provide two methods to further define the relation-
ship. We suggest further research into the spatial extent, timing, and
size limit of predation, as well as the importance of sturgeon to the
otter diet compared to other prey. These findings could help deter-
mine the extent of the predation and potential mitigation measures,
such as an altered release strateg y. River otter predation is just one
potential risk to the sur vival of hatchery-released juvenile Nechako
white sturgeon, and it is important to determine the extent of this
threat on the success of the conservation aquaculture program for
this at-risk population, as well as the potential risk to recruitment of
wild individuals.
We thank Steve McAdam, Mike Manky, Fraser Linza, Wayne
Salewski, the BC Ministr y of Forests, Lands, Natural Resource
Operations & Rural Development (FLNRORD), and the Freshwater
Fisheries Society of BC for support of the project. We additionally
thank Kyle Krahn, Mikayla More O'Ferrall, Zsolt Sary, Trevor Davies,
Jordan Cranmer, Rachel Pagdin, Skyler Fitzpatrick, and Parker Bosley
for assistance in the field. We also thank three anonymous reviewers
for their comments that improved the manuscript. We gratefully ac-
knowledge the financial support of the Province of British Columbia
through the Ministry of FLNRORD, with funding support provided
by Fisheries and Oceans Canada. Additional funding support was
provided by the Universit y of Northern British Columbia and an
NSERC Graduate Scholarship (CGS M) to CNB.
No conflict of interest has been declared by the authors.
We declare that there is no shared data related to this manuscript.
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How to cite this article: Babey CN, Gantner N, Williamson
CJ, Spendlow IE, Shrimpton JM. Evidence of predation of
juvenile white sturgeon (Acipenser transmontanus) by North
American river ot ter (Lontra canadensis) in the Nechako River,
British Columbia, Canada. J Appl Ichthyol 2020;0 0:1–5.
https://doi .org /10.1111/j ai.14114
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White Sturgeon, Acipenser transmontanus (WS), are distributed throughout three major river basins on the West Coast of North America: the Sacramento-San Joaquin, Columbia, and Fraser River drainages. Considered the largest North American freshwater fish, some WS use estuarine habitat and make limited marine movements between river basins. Some populations are listed by the United States or Canada as threatened or endangered (upper Columbia River above Grand Coulee Dam; Kootenai River; lower, middle and, upper Fraser River and Nechako River), while others do not warrant federal listing at this time (Sacramento-San Joaquin Rivers; Columbia River below Grand Coulee Dam; Snake River). Threats that impact WS throughout the species’ range include fishing effects and habitat alteration and degradation. Several populations suffer from recruitment limitations or collapse due to high early life mortality associated with these threats. Efforts to preserve WS populations include annual monitoring, harvest restrictions, habitat restoration, and conservation aquaculture. This paper provides a review of current knowledge on WS life history, ecology, physiology, behavior, and genetics and presents the status of WS in each drainage. Ongoing management and conservation efforts and additional research needs are identified to address present and future risks to the species.
Hans Kruuk's previous Wild Otters was the first, and until now the only, book to cover both natural history and scientific research on behaviour and ecology of otters in Europe. The present book is a revision, rewrite, and update, now covering all species of otter in North America as well as Europe and elsewhere. Aimed at naturalists, scientists, and conservationists, in a personal style and with many illustrations, it describes the ecology and behaviour of some of the most charismatic and enigmatic mammals in our environment, as well as the research to understand their particular ecological problems. With over 650 references, there is up-to-date description of the most recent studies, including feeding ecology, foraging behaviour, relationships with prey species, and factors that limit populations, as well as social and breeding behaviour, molecular genetics, energetics, the problems of exposure to cold water, mortality, effects of pollution, and the serious, recent conservation problems. There are enchanting direct observations of the animals, as well as guidance about how and where to watch and study them, and what are the most serious questions facing researchers. From otters in the British and American lakes and rivers, to sea otters in the Pacific ocean, giant otters in the Amazon and other species in Africa and Asia, this book provides an enthusiastic, critical, and thorough approach to their fascinating existence, the science needed to understand it, and the threats to their survival.
Since their first use in the mid-1980s, passive integrated transponder devices (PIT tags) have allowed innovative investigations into numerous biological traits of animals. The tiny, coded markers injected into individual animals allow assessment of growth rates, movement patterns, and survivorship for many species in a manner more reliable than traditional approaches of externally marking animals for identification. PIT tags have also been used to confirm the identity of zoo animals, pets, and protected species that have been illegally removed from the wild. New approaches with PIT tags herald advances in physiology and conservation biology, as well as greater understanding of social interactions among individuals in a population. Despite their current limitations, including high purchase cost, low detection distance, and potential tag loss in some circumstances, PIT tags offer many opportunities to unravel animal mysteries that heretofore could not be addressed effectively.
ABSTRACT River otters (Lontra canadensis) select specific habitat features when establishing latrines, but no studies have described latrine features in arid and semiarid environments. We developed a model describing those habitat features that influence otter latrine site selection on rivers in arid and semiarid watersheds of western Colorado, USA. River otters selected latrine sites with the presence of beaver (Castor canadensis) activity, large prominent rocks, adjacent to deeper water, with shading over the site, and rock or cliff overstory. Our model provides a robust predictive tool for identifying river otter latrine sites in arid environments of southwestern North America.