Trophic ecologies of double-crested cormorants and native piscivorous fishes in Lake Nipissing, Ontario
Bibliographic record
Abstract
Fisheries assessments have indicated a decline in Lake Nipissing’s walleye (Sander \nvitreus) population in recent decades. This has coincided with an increase in doublecrested cormorants (DCCO; Nannopterum auritum) on Lake Nipissing to conspicuous \nnumbers (3,000 nests in 2012), fueling concerns that cormorant predation may be \nadversely affecting walleye recovery. I used carbon and nitrogen stable isotope ratios \n(δ13C and δ15N, respectively) to examine the food web structure of Lake Nipissing, and in \nparticular, the role of DCCO predation and competition in relation to four other native \npiscivores; walleye, northern pike (Esox lucius), smallmouth bass (Micropterus \ndolomieu) and burbot (Lota lota). Trophic position (TP), estimated from δ15N, and \ntrophic niche size (SEAc), inferred from the dispersion of individuals in δ13C - δ15N \nisotopic space, were used to characterize piscivore niches. MixSIAR stable isotope \nmixing models (SIMM) were used to estimate the diet compositions of DCCO and \npiscivorous fishes. Among the piscivores, DCCO had the highest reliance on pelagic \nresources, the lowest trophic position, and the largest trophic niche size. Piscivorous \nfishes had higher levels of trophic niche overlap with each other than with DCCO. \nSIMMs predicted that DCCO diet was primarily composed of emerald shiner (Notropis \natherinoides) and logperch (Percina caprodes) with low proportions of all other prey \nfishes. Emerald shiner and logperch also dominated the diets of piscivorous fishes \nindicating dietary overlap with DCCO to some extent. Juvenile walleye were a relatively \nsmall proportion of the diets of both DCCO and piscivorous fishes based on SIMM \npredictions. Currently, there is no indication of limitations in Nipissing’s forage fish prey base so potential for interspecific competition is considered low. The low likelihood of \ntrophic niche overlap between DCCO and piscivorous fishes and the low contribution of \njuvenile walleye to DCCO diet suggests a low impact of DCCO predation on Nipissing’s \nrecovering walleye population. Stable isotope-based diet inference can complement bioenergetic models and other ecosystem assessment methods to improve our understanding \nof how DCCO interact with fish populations.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".