Reservoirs throughout the country exhibit degraded shorelines and simplified littoral habitats because of aging. This study evaluated the establishment of agricultural plantings on reservoir mudflats and the effectiveness of supplemental brush pile structures in providing recruitment habitat for juvenile fish. The mudflats of Enid Reservoir, Mississippi were seeded during the winter drawdown in October of 2016 and 2017 with agricultural plantings. Monitoring of plantings found grasses performed best in terms of establishment and providing potential fish habitat. During Summer 2017 brush piles and control sites, without brush, were sampled in Enid Reservoir using rotenone to evaluate juvenile fish use. Juvenile fish exhibited greater abundances and larger sizes, on average, in brush pile sites. Larger brush piles placed in shallower water provided the greatest benefit to juvenile fish.

The koi carp Cyprinus carpio is an invasive fish that has reached high numbers and biomass in the North Island of New Zealand, particularly in the Waikato region. This species has a variety of negative effects on aquatic ecosystems, increasing turbidity, uprooting aquatic macrophytes, and affecting water column nutrient levels. Recent research in Australia and New Zealand has shown that adult carp, though largely restricted to small scale movements, are capable of moving long distances. Movement in adult carp may be underestimated by these studies, and comparatively little is known about the movement of smaller carp. This study examined the feasibility of using laser ablation otolith microchemistry to track koi carp movement and identify spawning areas. Water samples from six locations (Lake Waahi, Lake Whangape, Lake Waikare, the Whangamarino River, and the Waikato River at Aka Aka and Rangiriri) were analysed using inductively coupled plasma mass spectrometry (ICP-MS). Significant differences between sites were found in the water concentrations of many elements. Koi carp were collected from the above locations, as well as from Opuatia Stream, Pungarehu Stream, the Maramarua River and Lake Hakanoa. The elemental concentrations in the asteriscus otoliths were analysed using laser ablation inductively coupled plasma mass spectrometry (LA‐ICP-MS). Elemental concentrations in the edges and nuclei of adult koi carp and the edges of young-of-the-year (YOY) koi carp were significantly different between capture sites. No significant differences were found in elemental concentrations between sites in the nuclei of YOY koi carp. A discriminant function analysis (DFA) was carried out using the otolith edge elemental signatures of koi carp. The model used Ba, Sr, Mg, Rb and Zn concentrations to differentiate between four capture locations: the Waikato River, Pungarehu Stream, Lake Waahi, and Lake Waikare and Pungarehu Stream. The DFA was able to correctly predict the capture location of 82% of koi carp using their otolith edge elemental signatures. The classification functions created using koi carp otolith edge signatures were then used as a training set to classify otolith nucleus signatures. The otolith nuclei of 80% of YOY koi carp were classified to their site of capture, suggesting they had not moved between locations. The majority of adult koi carp caught at Lake Waikare, Whangamarino River, Pungarehu Stream and Opuatia Stream had nucleus signatures matching their capture sites, indicating that these fish originated from their capture location. Koi carp from other sites likely moved there from another location. The majority of adult koi carp (88%) caught at the Waikato River at Rangiriri had otolith nucleus signatures matching Lake Waikare and Pungarehu Stream. Adult koi carp caught at Lake Waahi and the Waikato River at Aka Aka had otolith signatures corresponding to a range of locations. While some areas (Lake Waikare, Pungarehu Stream) appear to have resident koi carp populations that likely originated there, others (Lake Waahi, the Waikato River) appear to have koi carp populations of mixed origin. These results indicate that Lake Waikare, Pungarehu Stream and the Whangamarino River may be important sources of koi carp recruits in the lower Waikato region.

Marshes and seagrass beds have been widely recognized as important habitat for estuarine species, but less has been done on how these habitats interact and function together, thereby limiting understanding of the variability of juvenile recruitment to coastal systems. Therefore, the objective of this study was to assess the interaction between fringing marsh and adjacent seagrass for the provision of habitat for juvenile nekton. Weekly seine net and benthic seagrass core sampling from June to November 2020 determine the relationship between nekton and marsh-edge and seagrass habitat. This study shows disparate results, in terms of the effects of proximity to marsh edge and seagrass biomass on nekton abundance and size, pointing to different selectivity of marsh edge versus seagrass by different species. In addition, there are no effects of proximity to marsh edge and seagrass biomass on community composition, but an interactive effect on community dispersion.

<p dir="ltr">Fish population abundance and age structure is primarily determined through annual recruitment success (i.e., early life growth and survival through periods of heightened vulnerability). Many physical and biological processes contribute to fish early life growth and survival. Determining the relative contribution of these to annual recruitment variation is challenging owing to the multiple scales across which highly variable processes influence early life growth, mortality, and eventual survival. Elucidating these mechanisms are increasingly complicated by climate change and various anthropogenic stressors as conditions deviate from historic baselines. Thus, while traditional correlative approaches are often sufficient in explaining broad-scale patterns in historic recruitment variation, they are often unable to elicit processes at finer scales of potential importance and forecast future recruitment potential under climate change. Approaches that a) leverage mechanisms withstanding more than a century of research, and b) attempt to account for spatial and temporal scale-dependencies may promote a new understanding of conditions structuring annual patterns in recruitment and advance forecasting of future recruitment potential. Here, we used statistical and mechanistic modeling strategies to explore patterns in alewife and yellow perch recruitment in large lake ecosystems (i.e., the Laurentian Great Lakes). In chapter 2, we investigated nonstationary shifts in yellow perch stock-recruitment relationships in Saginaw Bay, Lake Huron. In chapter 3, we explore climate-induced physical transport phenologies of larval fish and consider the consequences of transport to experienced thermal conditions and encountered prey availability. Finally, in chapter 4, we investigated spatial scales of recruitment variation in a large lake to understand the relative influence of fine-scale asynchrony in structuring broader patterns in historic and potential future recruitment potential. </p>