Geology topics

T. Hook

Publications and source records attributed to T. Hook.

4 recordsLinked to original sources

USGS2022

An evaluation of fish spawning on degraded and remnant reefs in Saginaw Bay, Lake Huron

Saginaw Bay is a shallow, nutrient-rich embayment in Lake Huron that historically had a complex network of natural rocky reefs. These reef habitats were used as spawning and nursery areas for a variety of fish species, but decades of land-use related sedimentation caused many of these reefs to be degraded. Our study objectives were to analyze abiotic and biotic conditions on degraded and remnant reefs and describe spawning patterns of walleye ( Sander vitreus ) and lake whitefish ( Coregonus clupeaformis ) at these sites to determine the potential for increased utilization following reef restoration. During fall and spring 2014–2016, we evaluated water quality and egg predation at four sites with varying levels of reef degradation. Further, we documented reproductive utilization through capture of spawning adults and quantification of egg deposition. Walleye and lake whitefish utilized multiple sites for reproduction; however, densities of spawners and deposited eggs were low, suggesting that they were not utilizing study sites as major spawning locations. Walleye and lake whitefish eggs were eaten by multiple fish species, including larger fish such as channel catfish ( Ictalurus punctatus ). Dissolved oxygen levels were adequate (i.e., >7 mg 0 2 L −1 ) during spring walleye egg incubation; however, bottom dissolved oxygen levels became very low at some sites during winter ice cover, coinciding with lake whitefish egg incubation. As restoration of rocky reefs proceeds in the Bay, evidence of remnant reef spawning fish bodes well for long-term success, though potential limiting factors such as low dissolved oxygen, sedimentation, and egg predation require continued monitoring.

Michigan↗

USGS2020

Assessment of two techniques for remediation of lacustrine rocky reef spawning habitat

Rocky reef habitats in lacustrine systems constitute important areas for lithophilic‐spawning fishes. Interstitial spaces created by the structure of rocky reefs form microenvironments where incubating embryos and juvenile fish are potentially protected from predators and physical displacement. However, if interstitial spaces are filled or blocked by sediment or biofouling, the reef structure may lose these benefits. Common practices to restore reef habitat include augmentation of existing reef structures or construction of new reefs, though these practices can be costly. We explored an alternative approach for reef remediation. In 2018, we developed two benthic sled cleaning devices that used either propulsion or pressurized water jets and were towed behind a small vessel to clean reefs. We used the devices to clean two impaired natural rocky reefs in Saginaw Bay, Lake Huron. We indexed effectiveness of cleaning by measured changes in substrate relative hardness before and after cleaning. A biological response to reef cleaning was also measured by egg deposition of fall (Lake Whitefish Coregonus clupeaformis ) and spring (Walleye Sander vitreus ) lithophilic spawners. We found that our propulsion cleaning device was more effective in increasing substrate relative hardness than was the water jet device, although this was not consistent among all study locations. We also found that egg deposition on study plots was variable, but in general, egg deposition was highest on study plots that had the greatest increases in relative hardness post‐cleaning. The practicality of cleaning devices is likely related to the magnitude of site‐specific degradation. Our results indicate that the use of these or similar devices can potentially increase the quality of spawning habitat by displacing sediments that have deposited on reef structures.

North American Journal of Fisheries Management↗

USGS2020

Review of methods to repair and maintain lithophilic fish spawning habitat

Rocky reefs provide important spawning and refuge habitats for lithophilic spawning fishes. However, many reefs have been lost or severely degraded through anthropogenic effects like dredging, channelization, or sedimentation. Constructed reefs have been used to mitigate these effects in some systems, but these reefs are also subject to degradation which may warrant custodial maintenance. Monitoring and maintenance of natural or constructed spawning reefs are not common practices; therefore, few methodologies have been created to test the effectiveness of such tools. We conducted a literature review to assess available information on maintenance of rocky spawning habitats used by lithophilic fishes. We identified 54 rocky spawning habitat maintenance projects, most of which aimed to improve fish spawning habitats through the addition of spawning substrate ( n = 33) or cleaning of substrate ( n = 23). In comparison to shallow riverine studies focused on salmonids, we found little information on deep-water reefs, marine reefs, or other fish species. We discuss the possible application of potential spawning habitat cleaning methods from other disciplines (e.g., treasure hunting; archeology) that may provide effective means of reef maintenance that can be used by restoration practitioners.

Water↗

USGS2019

The effect of sediment cover and female characteristics on the hatching success of walleye

Natural and anthropogenic sources of sedimentation have the potential to degrade spawning habitat and negatively affect incubating fish embryos. Walleye Sander vitreus are lithophilic broadcast spawners that use specific spawning habitats that are vulnerable to degradation caused by deposition of suspended sediments. We measured the effect of different types of sediment cover on hatching success of Walleye eggs and assessed whether differences in female Walleye (female length and mean egg size) account for tolerance to sediment cover. Experiments were carried out in 2018 to test the effect of sediment cover on hatching success and in 2019 to test how female identity and female length or mean egg size may interact with sediment cover to influence hatching success. Eggs in both experiments were exposed to instantaneous sediment cover (0–7 mm) of either sand or silt from fertilization until day 15 of incubation. Results indicated that Walleye eggs were sensitive to silt cover (71% mortality with 2 mm of silt cover) but not sand cover (47% mortality with 7 mm of sand cover). Hatching success differed significantly among individual females. Although there was an indication that hatching success was marginally negatively related to female length and positively related to mean egg size, sediment cover seemed to have similar effects on eggs, regardless of female length or egg size. Susceptibility of Walleye eggs to mortality caused by sediment cover further underscores the need to limit large‐scale sediment loading and resuspension in aquatic systems.

Indiana↗